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cpython/Lib/decimal.py
Guido van Rossum da5b701aee Get rid of __context__, per the latest changes to PEP 343 and python-dev 
discussion.
There are two places of documentation that still mention __context__:
Doc/lib/libstdtypes.tex -- I wasn't quite sure how to rewrite that without
spending a whole lot of time thinking about it; and whatsnew, which Andrew
usually likes to change himself.
2006-05-02 19:47:52 +00:00

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# Copyright (c) 2004 Python Software Foundation.
# All rights reserved.
# Written by Eric Price <eprice at tjhsst.edu>
# and Facundo Batista <facundo at taniquetil.com.ar>
# and Raymond Hettinger <python at rcn.com>
# and Aahz <aahz at pobox.com>
# and Tim Peters
# This module is currently Py2.3 compatible and should be kept that way
# unless a major compelling advantage arises. IOW, 2.3 compatibility is
# strongly preferred, but not guaranteed.
# Also, this module should be kept in sync with the latest updates of
# the IBM specification as it evolves. Those updates will be treated
# as bug fixes (deviation from the spec is a compatibility, usability
# bug) and will be backported. At this point the spec is stabilizing
# and the updates are becoming fewer, smaller, and less significant.
"""
This is a Py2.3 implementation of decimal floating point arithmetic based on
the General Decimal Arithmetic Specification:
www2.hursley.ibm.com/decimal/decarith.html
and IEEE standard 854-1987:
www.cs.berkeley.edu/~ejr/projects/754/private/drafts/854-1987/dir.html
Decimal floating point has finite precision with arbitrarily large bounds.
The purpose of the module is to support arithmetic using familiar
"schoolhouse" rules and to avoid the some of tricky representation
issues associated with binary floating point. The package is especially
useful for financial applications or for contexts where users have
expectations that are at odds with binary floating point (for instance,
in binary floating point, 1.00 % 0.1 gives 0.09999999999999995 instead
of the expected Decimal("0.00") returned by decimal floating point).
Here are some examples of using the decimal module:
>>> from decimal import *
>>> setcontext(ExtendedContext)
>>> Decimal(0)
Decimal("0")
>>> Decimal("1")
Decimal("1")
>>> Decimal("-.0123")
Decimal("-0.0123")
>>> Decimal(123456)
Decimal("123456")
>>> Decimal("123.45e12345678901234567890")
Decimal("1.2345E+12345678901234567892")
>>> Decimal("1.33") + Decimal("1.27")
Decimal("2.60")
>>> Decimal("12.34") + Decimal("3.87") - Decimal("18.41")
Decimal("-2.20")
>>> dig = Decimal(1)
>>> print dig / Decimal(3)
0.333333333
>>> getcontext().prec = 18
>>> print dig / Decimal(3)
0.333333333333333333
>>> print dig.sqrt()
1
>>> print Decimal(3).sqrt()
1.73205080756887729
>>> print Decimal(3) ** 123
4.85192780976896427E+58
>>> inf = Decimal(1) / Decimal(0)
>>> print inf
Infinity
>>> neginf = Decimal(-1) / Decimal(0)
>>> print neginf
-Infinity
>>> print neginf + inf
NaN
>>> print neginf * inf
-Infinity
>>> print dig / 0
Infinity
>>> getcontext().traps[DivisionByZero] = 1
>>> print dig / 0
Traceback (most recent call last):
...
...
...
DivisionByZero: x / 0
>>> c = Context()
>>> c.traps[InvalidOperation] = 0
>>> print c.flags[InvalidOperation]
0
>>> c.divide(Decimal(0), Decimal(0))
Decimal("NaN")
>>> c.traps[InvalidOperation] = 1
>>> print c.flags[InvalidOperation]
1
>>> c.flags[InvalidOperation] = 0
>>> print c.flags[InvalidOperation]
0
>>> print c.divide(Decimal(0), Decimal(0))
Traceback (most recent call last):
...
...
...
InvalidOperation: 0 / 0
>>> print c.flags[InvalidOperation]
1
>>> c.flags[InvalidOperation] = 0
>>> c.traps[InvalidOperation] = 0
>>> print c.divide(Decimal(0), Decimal(0))
NaN
>>> print c.flags[InvalidOperation]
1
>>>
"""
__all__ = [
# Two major classes
'Decimal', 'Context',
# Contexts
'DefaultContext', 'BasicContext', 'ExtendedContext',
# Exceptions
'DecimalException', 'Clamped', 'InvalidOperation', 'DivisionByZero',
'Inexact', 'Rounded', 'Subnormal', 'Overflow', 'Underflow',
# Constants for use in setting up contexts
'ROUND_DOWN', 'ROUND_HALF_UP', 'ROUND_HALF_EVEN', 'ROUND_CEILING',
'ROUND_FLOOR', 'ROUND_UP', 'ROUND_HALF_DOWN',
# Functions for manipulating contexts
'setcontext', 'getcontext'
]
import copy as _copy
#Rounding
ROUND_DOWN = 'ROUND_DOWN'
ROUND_HALF_UP = 'ROUND_HALF_UP'
ROUND_HALF_EVEN = 'ROUND_HALF_EVEN'
ROUND_CEILING = 'ROUND_CEILING'
ROUND_FLOOR = 'ROUND_FLOOR'
ROUND_UP = 'ROUND_UP'
ROUND_HALF_DOWN = 'ROUND_HALF_DOWN'
#Rounding decision (not part of the public API)
NEVER_ROUND = 'NEVER_ROUND' # Round in division (non-divmod), sqrt ONLY
ALWAYS_ROUND = 'ALWAYS_ROUND' # Every operation rounds at end.
#Errors
class DecimalException(ArithmeticError):
"""Base exception class.
Used exceptions derive from this.
If an exception derives from another exception besides this (such as
Underflow (Inexact, Rounded, Subnormal) that indicates that it is only
called if the others are present. This isn't actually used for
anything, though.
handle -- Called when context._raise_error is called and the
trap_enabler is set. First argument is self, second is the
context. More arguments can be given, those being after
the explanation in _raise_error (For example,
context._raise_error(NewError, '(-x)!', self._sign) would
call NewError().handle(context, self._sign).)
To define a new exception, it should be sufficient to have it derive
from DecimalException.
"""
def handle(self, context, *args):
pass
class Clamped(DecimalException):
"""Exponent of a 0 changed to fit bounds.
This occurs and signals clamped if the exponent of a result has been
altered in order to fit the constraints of a specific concrete
representation. This may occur when the exponent of a zero result would
be outside the bounds of a representation, or when a large normal
number would have an encoded exponent that cannot be represented. In
this latter case, the exponent is reduced to fit and the corresponding
number of zero digits are appended to the coefficient ("fold-down").
"""
class InvalidOperation(DecimalException):
"""An invalid operation was performed.
Various bad things cause this:
Something creates a signaling NaN
-INF + INF
0 * (+-)INF
(+-)INF / (+-)INF
x % 0
(+-)INF % x
x._rescale( non-integer )
sqrt(-x) , x > 0
0 ** 0
x ** (non-integer)
x ** (+-)INF
An operand is invalid
"""
def handle(self, context, *args):
if args:
if args[0] == 1: #sNaN, must drop 's' but keep diagnostics
return Decimal( (args[1]._sign, args[1]._int, 'n') )
return NaN
class ConversionSyntax(InvalidOperation):
"""Trying to convert badly formed string.
This occurs and signals invalid-operation if an string is being
converted to a number and it does not conform to the numeric string
syntax. The result is [0,qNaN].
"""
def handle(self, context, *args):
return (0, (0,), 'n') #Passed to something which uses a tuple.
class DivisionByZero(DecimalException, ZeroDivisionError):
"""Division by 0.
This occurs and signals division-by-zero if division of a finite number
by zero was attempted (during a divide-integer or divide operation, or a
power operation with negative right-hand operand), and the dividend was
not zero.
The result of the operation is [sign,inf], where sign is the exclusive
or of the signs of the operands for divide, or is 1 for an odd power of
-0, for power.
"""
def handle(self, context, sign, double = None, *args):
if double is not None:
return (Infsign[sign],)*2
return Infsign[sign]
class DivisionImpossible(InvalidOperation):
"""Cannot perform the division adequately.
This occurs and signals invalid-operation if the integer result of a
divide-integer or remainder operation had too many digits (would be
longer than precision). The result is [0,qNaN].
"""
def handle(self, context, *args):
return (NaN, NaN)
class DivisionUndefined(InvalidOperation, ZeroDivisionError):
"""Undefined result of division.
This occurs and signals invalid-operation if division by zero was
attempted (during a divide-integer, divide, or remainder operation), and
the dividend is also zero. The result is [0,qNaN].
"""
def handle(self, context, tup=None, *args):
if tup is not None:
return (NaN, NaN) #for 0 %0, 0 // 0
return NaN
class Inexact(DecimalException):
"""Had to round, losing information.
This occurs and signals inexact whenever the result of an operation is
not exact (that is, it needed to be rounded and any discarded digits
were non-zero), or if an overflow or underflow condition occurs. The
result in all cases is unchanged.
The inexact signal may be tested (or trapped) to determine if a given
operation (or sequence of operations) was inexact.
"""
pass
class InvalidContext(InvalidOperation):
"""Invalid context. Unknown rounding, for example.
This occurs and signals invalid-operation if an invalid context was
detected during an operation. This can occur if contexts are not checked
on creation and either the precision exceeds the capability of the
underlying concrete representation or an unknown or unsupported rounding
was specified. These aspects of the context need only be checked when
the values are required to be used. The result is [0,qNaN].
"""
def handle(self, context, *args):
return NaN
class Rounded(DecimalException):
"""Number got rounded (not necessarily changed during rounding).
This occurs and signals rounded whenever the result of an operation is
rounded (that is, some zero or non-zero digits were discarded from the
coefficient), or if an overflow or underflow condition occurs. The
result in all cases is unchanged.
The rounded signal may be tested (or trapped) to determine if a given
operation (or sequence of operations) caused a loss of precision.
"""
pass
class Subnormal(DecimalException):
"""Exponent < Emin before rounding.
This occurs and signals subnormal whenever the result of a conversion or
operation is subnormal (that is, its adjusted exponent is less than
Emin, before any rounding). The result in all cases is unchanged.
The subnormal signal may be tested (or trapped) to determine if a given
or operation (or sequence of operations) yielded a subnormal result.
"""
pass
class Overflow(Inexact, Rounded):
"""Numerical overflow.
This occurs and signals overflow if the adjusted exponent of a result
(from a conversion or from an operation that is not an attempt to divide
by zero), after rounding, would be greater than the largest value that
can be handled by the implementation (the value Emax).
The result depends on the rounding mode:
For round-half-up and round-half-even (and for round-half-down and
round-up, if implemented), the result of the operation is [sign,inf],
where sign is the sign of the intermediate result. For round-down, the
result is the largest finite number that can be represented in the
current precision, with the sign of the intermediate result. For
round-ceiling, the result is the same as for round-down if the sign of
the intermediate result is 1, or is [0,inf] otherwise. For round-floor,
the result is the same as for round-down if the sign of the intermediate
result is 0, or is [1,inf] otherwise. In all cases, Inexact and Rounded
will also be raised.
"""
def handle(self, context, sign, *args):
if context.rounding in (ROUND_HALF_UP, ROUND_HALF_EVEN,
ROUND_HALF_DOWN, ROUND_UP):
return Infsign[sign]
if sign == 0:
if context.rounding == ROUND_CEILING:
return Infsign[sign]
return Decimal((sign, (9,)*context.prec,
context.Emax-context.prec+1))
if sign == 1:
if context.rounding == ROUND_FLOOR:
return Infsign[sign]
return Decimal( (sign, (9,)*context.prec,
context.Emax-context.prec+1))
class Underflow(Inexact, Rounded, Subnormal):
"""Numerical underflow with result rounded to 0.
This occurs and signals underflow if a result is inexact and the
adjusted exponent of the result would be smaller (more negative) than
the smallest value that can be handled by the implementation (the value
Emin). That is, the result is both inexact and subnormal.
The result after an underflow will be a subnormal number rounded, if
necessary, so that its exponent is not less than Etiny. This may result
in 0 with the sign of the intermediate result and an exponent of Etiny.
In all cases, Inexact, Rounded, and Subnormal will also be raised.
"""
# List of public traps and flags
_signals = [Clamped, DivisionByZero, Inexact, Overflow, Rounded,
Underflow, InvalidOperation, Subnormal]
# Map conditions (per the spec) to signals
_condition_map = {ConversionSyntax:InvalidOperation,
DivisionImpossible:InvalidOperation,
DivisionUndefined:InvalidOperation,
InvalidContext:InvalidOperation}
##### Context Functions #######################################
# The getcontext() and setcontext() function manage access to a thread-local
# current context. Py2.4 offers direct support for thread locals. If that
# is not available, use threading.currentThread() which is slower but will
# work for older Pythons. If threads are not part of the build, create a
# mock threading object with threading.local() returning the module namespace.
try:
import threading
except ImportError:
# Python was compiled without threads; create a mock object instead
import sys
class MockThreading:
def local(self, sys=sys):
return sys.modules[__name__]
threading = MockThreading()
del sys, MockThreading
try:
threading.local
except AttributeError:
#To fix reloading, force it to create a new context
#Old contexts have different exceptions in their dicts, making problems.
if hasattr(threading.currentThread(), '__decimal_context__'):
del threading.currentThread().__decimal_context__
def setcontext(context):
"""Set this thread's context to context."""
if context in (DefaultContext, BasicContext, ExtendedContext):
context = context.copy()
context.clear_flags()
threading.currentThread().__decimal_context__ = context
def getcontext():
"""Returns this thread's context.
If this thread does not yet have a context, returns
a new context and sets this thread's context.
New contexts are copies of DefaultContext.
"""
try:
return threading.currentThread().__decimal_context__
except AttributeError:
context = Context()
threading.currentThread().__decimal_context__ = context
return context
else:
local = threading.local()
if hasattr(local, '__decimal_context__'):
del local.__decimal_context__
def getcontext(_local=local):
"""Returns this thread's context.
If this thread does not yet have a context, returns
a new context and sets this thread's context.
New contexts are copies of DefaultContext.
"""
try:
return _local.__decimal_context__
except AttributeError:
context = Context()
_local.__decimal_context__ = context
return context
def setcontext(context, _local=local):
"""Set this thread's context to context."""
if context in (DefaultContext, BasicContext, ExtendedContext):
context = context.copy()
context.clear_flags()
_local.__decimal_context__ = context
del threading, local # Don't contaminate the namespace
##### Decimal class ###########################################
class Decimal(object):
"""Floating point class for decimal arithmetic."""
__slots__ = ('_exp','_int','_sign', '_is_special')
# Generally, the value of the Decimal instance is given by
# (-1)**_sign * _int * 10**_exp
# Special values are signified by _is_special == True
# We're immutable, so use __new__ not __init__
def __new__(cls, value="0", context=None):
"""Create a decimal point instance.
>>> Decimal('3.14') # string input
Decimal("3.14")
>>> Decimal((0, (3, 1, 4), -2)) # tuple input (sign, digit_tuple, exponent)
Decimal("3.14")
>>> Decimal(314) # int or long
Decimal("314")
>>> Decimal(Decimal(314)) # another decimal instance
Decimal("314")
"""
self = object.__new__(cls)
self._is_special = False
# From an internal working value
if isinstance(value, _WorkRep):
self._sign = value.sign
self._int = tuple(map(int, str(value.int)))
self._exp = int(value.exp)
return self
# From another decimal
if isinstance(value, Decimal):
self._exp = value._exp
self._sign = value._sign
self._int = value._int
self._is_special = value._is_special
return self
# From an integer
if isinstance(value, (int,long)):
if value >= 0:
self._sign = 0
else:
self._sign = 1
self._exp = 0
self._int = tuple(map(int, str(abs(value))))
return self
# tuple/list conversion (possibly from as_tuple())
if isinstance(value, (list,tuple)):
if len(value) != 3:
raise ValueError, 'Invalid arguments'
if value[0] not in (0,1):
raise ValueError, 'Invalid sign'
for digit in value[1]:
if not isinstance(digit, (int,long)) or digit < 0:
raise ValueError, "The second value in the tuple must be composed of non negative integer elements."
self._sign = value[0]
self._int = tuple(value[1])
if value[2] in ('F','n','N'):
self._exp = value[2]
self._is_special = True
else:
self._exp = int(value[2])
return self
if isinstance(value, float):
raise TypeError("Cannot convert float to Decimal. " +
"First convert the float to a string")
# Other argument types may require the context during interpretation
if context is None:
context = getcontext()
# From a string
# REs insist on real strings, so we can too.
if isinstance(value, basestring):
if _isinfinity(value):
self._exp = 'F'
self._int = (0,)
self._is_special = True
if _isinfinity(value) == 1:
self._sign = 0
else:
self._sign = 1
return self
if _isnan(value):
sig, sign, diag = _isnan(value)
self._is_special = True
if len(diag) > context.prec: #Diagnostic info too long
self._sign, self._int, self._exp = \
context._raise_error(ConversionSyntax)
return self
if sig == 1:
self._exp = 'n' #qNaN
else: #sig == 2
self._exp = 'N' #sNaN
self._sign = sign
self._int = tuple(map(int, diag)) #Diagnostic info
return self
try:
self._sign, self._int, self._exp = _string2exact(value)
except ValueError:
self._is_special = True
self._sign, self._int, self._exp = context._raise_error(ConversionSyntax)
return self
raise TypeError("Cannot convert %r to Decimal" % value)
def _isnan(self):
"""Returns whether the number is not actually one.
0 if a number
1 if NaN
2 if sNaN
"""
if self._is_special:
exp = self._exp
if exp == 'n':
return 1
elif exp == 'N':
return 2
return 0
def _isinfinity(self):
"""Returns whether the number is infinite
0 if finite or not a number
1 if +INF
-1 if -INF
"""
if self._exp == 'F':
if self._sign:
return -1
return 1
return 0
def _check_nans(self, other = None, context=None):
"""Returns whether the number is not actually one.
if self, other are sNaN, signal
if self, other are NaN return nan
return 0
Done before operations.
"""
self_is_nan = self._isnan()
if other is None:
other_is_nan = False
else:
other_is_nan = other._isnan()
if self_is_nan or other_is_nan:
if context is None:
context = getcontext()
if self_is_nan == 2:
return context._raise_error(InvalidOperation, 'sNaN',
1, self)
if other_is_nan == 2:
return context._raise_error(InvalidOperation, 'sNaN',
1, other)
if self_is_nan:
return self
return other
return 0
def __nonzero__(self):
"""Is the number non-zero?
0 if self == 0
1 if self != 0
"""
if self._is_special:
return 1
return sum(self._int) != 0
def __cmp__(self, other, context=None):
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
return 1 # Comparison involving NaN's always reports self > other
# INF = INF
return cmp(self._isinfinity(), other._isinfinity())
if not self and not other:
return 0 #If both 0, sign comparison isn't certain.
#If different signs, neg one is less
if other._sign < self._sign:
return -1
if self._sign < other._sign:
return 1
self_adjusted = self.adjusted()
other_adjusted = other.adjusted()
if self_adjusted == other_adjusted and \
self._int + (0,)*(self._exp - other._exp) == \
other._int + (0,)*(other._exp - self._exp):
return 0 #equal, except in precision. ([0]*(-x) = [])
elif self_adjusted > other_adjusted and self._int[0] != 0:
return (-1)**self._sign
elif self_adjusted < other_adjusted and other._int[0] != 0:
return -((-1)**self._sign)
# Need to round, so make sure we have a valid context
if context is None:
context = getcontext()
context = context._shallow_copy()
rounding = context._set_rounding(ROUND_UP) #round away from 0
flags = context._ignore_all_flags()
res = self.__sub__(other, context=context)
context._regard_flags(*flags)
context.rounding = rounding
if not res:
return 0
elif res._sign:
return -1
return 1
def __eq__(self, other):
if not isinstance(other, (Decimal, int, long)):
return NotImplemented
return self.__cmp__(other) == 0
def __ne__(self, other):
if not isinstance(other, (Decimal, int, long)):
return NotImplemented
return self.__cmp__(other) != 0
def compare(self, other, context=None):
"""Compares one to another.
-1 => a < b
0 => a = b
1 => a > b
NaN => one is NaN
Like __cmp__, but returns Decimal instances.
"""
other = _convert_other(other)
if other is NotImplemented:
return other
#compare(NaN, NaN) = NaN
if (self._is_special or other and other._is_special):
ans = self._check_nans(other, context)
if ans:
return ans
return Decimal(self.__cmp__(other, context))
def __hash__(self):
"""x.__hash__() <==> hash(x)"""
# Decimal integers must hash the same as the ints
# Non-integer decimals are normalized and hashed as strings
# Normalization assures that hast(100E-1) == hash(10)
if self._is_special:
if self._isnan():
raise TypeError('Cannot hash a NaN value.')
return hash(str(self))
i = int(self)
if self == Decimal(i):
return hash(i)
assert self.__nonzero__() # '-0' handled by integer case
return hash(str(self.normalize()))
def as_tuple(self):
"""Represents the number as a triple tuple.
To show the internals exactly as they are.
"""
return (self._sign, self._int, self._exp)
def __repr__(self):
"""Represents the number as an instance of Decimal."""
# Invariant: eval(repr(d)) == d
return 'Decimal("%s")' % str(self)
def __str__(self, eng = 0, context=None):
"""Return string representation of the number in scientific notation.
Captures all of the information in the underlying representation.
"""
if self._is_special:
if self._isnan():
minus = '-'*self._sign
if self._int == (0,):
info = ''
else:
info = ''.join(map(str, self._int))
if self._isnan() == 2:
return minus + 'sNaN' + info
return minus + 'NaN' + info
if self._isinfinity():
minus = '-'*self._sign
return minus + 'Infinity'
if context is None:
context = getcontext()
tmp = map(str, self._int)
numdigits = len(self._int)
leftdigits = self._exp + numdigits
if eng and not self: #self = 0eX wants 0[.0[0]]eY, not [[0]0]0eY
if self._exp < 0 and self._exp >= -6: #short, no need for e/E
s = '-'*self._sign + '0.' + '0'*(abs(self._exp))
return s
#exp is closest mult. of 3 >= self._exp
exp = ((self._exp - 1)// 3 + 1) * 3
if exp != self._exp:
s = '0.'+'0'*(exp - self._exp)
else:
s = '0'
if exp != 0:
if context.capitals:
s += 'E'
else:
s += 'e'
if exp > 0:
s += '+' #0.0e+3, not 0.0e3
s += str(exp)
s = '-'*self._sign + s
return s
if eng:
dotplace = (leftdigits-1)%3+1
adjexp = leftdigits -1 - (leftdigits-1)%3
else:
adjexp = leftdigits-1
dotplace = 1
if self._exp == 0:
pass
elif self._exp < 0 and adjexp >= 0:
tmp.insert(leftdigits, '.')
elif self._exp < 0 and adjexp >= -6:
tmp[0:0] = ['0'] * int(-leftdigits)
tmp.insert(0, '0.')
else:
if numdigits > dotplace:
tmp.insert(dotplace, '.')
elif numdigits < dotplace:
tmp.extend(['0']*(dotplace-numdigits))
if adjexp:
if not context.capitals:
tmp.append('e')
else:
tmp.append('E')
if adjexp > 0:
tmp.append('+')
tmp.append(str(adjexp))
if eng:
while tmp[0:1] == ['0']:
tmp[0:1] = []
if len(tmp) == 0 or tmp[0] == '.' or tmp[0].lower() == 'e':
tmp[0:0] = ['0']
if self._sign:
tmp.insert(0, '-')
return ''.join(tmp)
def to_eng_string(self, context=None):
"""Convert to engineering-type string.
Engineering notation has an exponent which is a multiple of 3, so there
are up to 3 digits left of the decimal place.
Same rules for when in exponential and when as a value as in __str__.
"""
return self.__str__(eng=1, context=context)
def __neg__(self, context=None):
"""Returns a copy with the sign switched.
Rounds, if it has reason.
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
if not self:
# -Decimal('0') is Decimal('0'), not Decimal('-0')
sign = 0
elif self._sign:
sign = 0
else:
sign = 1
if context is None:
context = getcontext()
if context._rounding_decision == ALWAYS_ROUND:
return Decimal((sign, self._int, self._exp))._fix(context)
return Decimal( (sign, self._int, self._exp))
def __pos__(self, context=None):
"""Returns a copy, unless it is a sNaN.
Rounds the number (if more then precision digits)
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
sign = self._sign
if not self:
# + (-0) = 0
sign = 0
if context is None:
context = getcontext()
if context._rounding_decision == ALWAYS_ROUND:
ans = self._fix(context)
else:
ans = Decimal(self)
ans._sign = sign
return ans
def __abs__(self, round=1, context=None):
"""Returns the absolute value of self.
If the second argument is 0, do not round.
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
if not round:
if context is None:
context = getcontext()
context = context._shallow_copy()
context._set_rounding_decision(NEVER_ROUND)
if self._sign:
ans = self.__neg__(context=context)
else:
ans = self.__pos__(context=context)
return ans
def __add__(self, other, context=None):
"""Returns self + other.
-INF + INF (or the reverse) cause InvalidOperation errors.
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if context is None:
context = getcontext()
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
return ans
if self._isinfinity():
#If both INF, same sign => same as both, opposite => error.
if self._sign != other._sign and other._isinfinity():
return context._raise_error(InvalidOperation, '-INF + INF')
return Decimal(self)
if other._isinfinity():
return Decimal(other) #Can't both be infinity here
shouldround = context._rounding_decision == ALWAYS_ROUND
exp = min(self._exp, other._exp)
negativezero = 0
if context.rounding == ROUND_FLOOR and self._sign != other._sign:
#If the answer is 0, the sign should be negative, in this case.
negativezero = 1
if not self and not other:
sign = min(self._sign, other._sign)
if negativezero:
sign = 1
return Decimal( (sign, (0,), exp))
if not self:
exp = max(exp, other._exp - context.prec-1)
ans = other._rescale(exp, watchexp=0, context=context)
if shouldround:
ans = ans._fix(context)
return ans
if not other:
exp = max(exp, self._exp - context.prec-1)
ans = self._rescale(exp, watchexp=0, context=context)
if shouldround:
ans = ans._fix(context)
return ans
op1 = _WorkRep(self)
op2 = _WorkRep(other)
op1, op2 = _normalize(op1, op2, shouldround, context.prec)
result = _WorkRep()
if op1.sign != op2.sign:
# Equal and opposite
if op1.int == op2.int:
if exp < context.Etiny():
exp = context.Etiny()
context._raise_error(Clamped)
return Decimal((negativezero, (0,), exp))
if op1.int < op2.int:
op1, op2 = op2, op1
#OK, now abs(op1) > abs(op2)
if op1.sign == 1:
result.sign = 1
op1.sign, op2.sign = op2.sign, op1.sign
else:
result.sign = 0
#So we know the sign, and op1 > 0.
elif op1.sign == 1:
result.sign = 1
op1.sign, op2.sign = (0, 0)
else:
result.sign = 0
#Now, op1 > abs(op2) > 0
if op2.sign == 0:
result.int = op1.int + op2.int
else:
result.int = op1.int - op2.int
result.exp = op1.exp
ans = Decimal(result)
if shouldround:
ans = ans._fix(context)
return ans
__radd__ = __add__
def __sub__(self, other, context=None):
"""Return self + (-other)"""
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
ans = self._check_nans(other, context=context)
if ans:
return ans
# -Decimal(0) = Decimal(0), which we don't want since
# (-0 - 0 = -0 + (-0) = -0, but -0 + 0 = 0.)
# so we change the sign directly to a copy
tmp = Decimal(other)
tmp._sign = 1-tmp._sign
return self.__add__(tmp, context=context)
def __rsub__(self, other, context=None):
"""Return other + (-self)"""
other = _convert_other(other)
if other is NotImplemented:
return other
tmp = Decimal(self)
tmp._sign = 1 - tmp._sign
return other.__add__(tmp, context=context)
def _increment(self, round=1, context=None):
"""Special case of add, adding 1eExponent
Since it is common, (rounding, for example) this adds
(sign)*one E self._exp to the number more efficiently than add.
For example:
Decimal('5.624e10')._increment() == Decimal('5.625e10')
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
return Decimal(self) # Must be infinite, and incrementing makes no difference
L = list(self._int)
L[-1] += 1
spot = len(L)-1
while L[spot] == 10:
L[spot] = 0
if spot == 0:
L[0:0] = [1]
break
L[spot-1] += 1
spot -= 1
ans = Decimal((self._sign, L, self._exp))
if context is None:
context = getcontext()
if round and context._rounding_decision == ALWAYS_ROUND:
ans = ans._fix(context)
return ans
def __mul__(self, other, context=None):
"""Return self * other.
(+-) INF * 0 (or its reverse) raise InvalidOperation.
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if context is None:
context = getcontext()
resultsign = self._sign ^ other._sign
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
return ans
if self._isinfinity():
if not other:
return context._raise_error(InvalidOperation, '(+-)INF * 0')
return Infsign[resultsign]
if other._isinfinity():
if not self:
return context._raise_error(InvalidOperation, '0 * (+-)INF')
return Infsign[resultsign]
resultexp = self._exp + other._exp
shouldround = context._rounding_decision == ALWAYS_ROUND
# Special case for multiplying by zero
if not self or not other:
ans = Decimal((resultsign, (0,), resultexp))
if shouldround:
#Fixing in case the exponent is out of bounds
ans = ans._fix(context)
return ans
# Special case for multiplying by power of 10
if self._int == (1,):
ans = Decimal((resultsign, other._int, resultexp))
if shouldround:
ans = ans._fix(context)
return ans
if other._int == (1,):
ans = Decimal((resultsign, self._int, resultexp))
if shouldround:
ans = ans._fix(context)
return ans
op1 = _WorkRep(self)
op2 = _WorkRep(other)
ans = Decimal( (resultsign, map(int, str(op1.int * op2.int)), resultexp))
if shouldround:
ans = ans._fix(context)
return ans
__rmul__ = __mul__
def __div__(self, other, context=None):
"""Return self / other."""
return self._divide(other, context=context)
__truediv__ = __div__
def _divide(self, other, divmod = 0, context=None):
"""Return a / b, to context.prec precision.
divmod:
0 => true division
1 => (a //b, a%b)
2 => a //b
3 => a%b
Actually, if divmod is 2 or 3 a tuple is returned, but errors for
computing the other value are not raised.
"""
other = _convert_other(other)
if other is NotImplemented:
if divmod in (0, 1):
return NotImplemented
return (NotImplemented, NotImplemented)
if context is None:
context = getcontext()
sign = self._sign ^ other._sign
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
if divmod:
return (ans, ans)
return ans
if self._isinfinity() and other._isinfinity():
if divmod:
return (context._raise_error(InvalidOperation,
'(+-)INF // (+-)INF'),
context._raise_error(InvalidOperation,
'(+-)INF % (+-)INF'))
return context._raise_error(InvalidOperation, '(+-)INF/(+-)INF')
if self._isinfinity():
if divmod == 1:
return (Infsign[sign],
context._raise_error(InvalidOperation, 'INF % x'))
elif divmod == 2:
return (Infsign[sign], NaN)
elif divmod == 3:
return (Infsign[sign],
context._raise_error(InvalidOperation, 'INF % x'))
return Infsign[sign]
if other._isinfinity():
if divmod:
return (Decimal((sign, (0,), 0)), Decimal(self))
context._raise_error(Clamped, 'Division by infinity')
return Decimal((sign, (0,), context.Etiny()))
# Special cases for zeroes
if not self and not other:
if divmod:
return context._raise_error(DivisionUndefined, '0 / 0', 1)
return context._raise_error(DivisionUndefined, '0 / 0')
if not self:
if divmod:
otherside = Decimal(self)
otherside._exp = min(self._exp, other._exp)
return (Decimal((sign, (0,), 0)), otherside)
exp = self._exp - other._exp
if exp < context.Etiny():
exp = context.Etiny()
context._raise_error(Clamped, '0e-x / y')
if exp > context.Emax:
exp = context.Emax
context._raise_error(Clamped, '0e+x / y')
return Decimal( (sign, (0,), exp) )
if not other:
if divmod:
return context._raise_error(DivisionByZero, 'divmod(x,0)',
sign, 1)
return context._raise_error(DivisionByZero, 'x / 0', sign)
#OK, so neither = 0, INF or NaN
shouldround = context._rounding_decision == ALWAYS_ROUND
#If we're dividing into ints, and self < other, stop.
#self.__abs__(0) does not round.
if divmod and (self.__abs__(0, context) < other.__abs__(0, context)):
if divmod == 1 or divmod == 3:
exp = min(self._exp, other._exp)
ans2 = self._rescale(exp, context=context, watchexp=0)
if shouldround:
ans2 = ans2._fix(context)
return (Decimal( (sign, (0,), 0) ),
ans2)
elif divmod == 2:
#Don't round the mod part, if we don't need it.
return (Decimal( (sign, (0,), 0) ), Decimal(self))
op1 = _WorkRep(self)
op2 = _WorkRep(other)
op1, op2, adjust = _adjust_coefficients(op1, op2)
res = _WorkRep( (sign, 0, (op1.exp - op2.exp)) )
if divmod and res.exp > context.prec + 1:
return context._raise_error(DivisionImpossible)
prec_limit = 10 ** context.prec
while 1:
while op2.int <= op1.int:
res.int += 1
op1.int -= op2.int
if res.exp == 0 and divmod:
if res.int >= prec_limit and shouldround:
return context._raise_error(DivisionImpossible)
otherside = Decimal(op1)
frozen = context._ignore_all_flags()
exp = min(self._exp, other._exp)
otherside = otherside._rescale(exp, context=context, watchexp=0)
context._regard_flags(*frozen)
if shouldround:
otherside = otherside._fix(context)
return (Decimal(res), otherside)
if op1.int == 0 and adjust >= 0 and not divmod:
break
if res.int >= prec_limit and shouldround:
if divmod:
return context._raise_error(DivisionImpossible)
shouldround=1
# Really, the answer is a bit higher, so adding a one to
# the end will make sure the rounding is right.
if op1.int != 0:
res.int *= 10
res.int += 1
res.exp -= 1
break
res.int *= 10
res.exp -= 1
adjust += 1
op1.int *= 10
op1.exp -= 1
if res.exp == 0 and divmod and op2.int > op1.int:
#Solves an error in precision. Same as a previous block.
if res.int >= prec_limit and shouldround:
return context._raise_error(DivisionImpossible)
otherside = Decimal(op1)
frozen = context._ignore_all_flags()
exp = min(self._exp, other._exp)
otherside = otherside._rescale(exp, context=context)
context._regard_flags(*frozen)
return (Decimal(res), otherside)
ans = Decimal(res)
if shouldround:
ans = ans._fix(context)
return ans
def __rdiv__(self, other, context=None):
"""Swaps self/other and returns __div__."""
other = _convert_other(other)
if other is NotImplemented:
return other
return other.__div__(self, context=context)
__rtruediv__ = __rdiv__
def __divmod__(self, other, context=None):
"""
(self // other, self % other)
"""
return self._divide(other, 1, context)
def __rdivmod__(self, other, context=None):
"""Swaps self/other and returns __divmod__."""
other = _convert_other(other)
if other is NotImplemented:
return other
return other.__divmod__(self, context=context)
def __mod__(self, other, context=None):
"""
self % other
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
return ans
if self and not other:
return context._raise_error(InvalidOperation, 'x % 0')
return self._divide(other, 3, context)[1]
def __rmod__(self, other, context=None):
"""Swaps self/other and returns __mod__."""
other = _convert_other(other)
if other is NotImplemented:
return other
return other.__mod__(self, context=context)
def remainder_near(self, other, context=None):
"""
Remainder nearest to 0- abs(remainder-near) <= other/2
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
ans = self._check_nans(other, context)
if ans:
return ans
if self and not other:
return context._raise_error(InvalidOperation, 'x % 0')
if context is None:
context = getcontext()
# If DivisionImpossible causes an error, do not leave Rounded/Inexact
# ignored in the calling function.
context = context._shallow_copy()
flags = context._ignore_flags(Rounded, Inexact)
#keep DivisionImpossible flags
(side, r) = self.__divmod__(other, context=context)
if r._isnan():
context._regard_flags(*flags)
return r
context = context._shallow_copy()
rounding = context._set_rounding_decision(NEVER_ROUND)
if other._sign:
comparison = other.__div__(Decimal(-2), context=context)
else:
comparison = other.__div__(Decimal(2), context=context)
context._set_rounding_decision(rounding)
context._regard_flags(*flags)
s1, s2 = r._sign, comparison._sign
r._sign, comparison._sign = 0, 0
if r < comparison:
r._sign, comparison._sign = s1, s2
#Get flags now
self.__divmod__(other, context=context)
return r._fix(context)
r._sign, comparison._sign = s1, s2
rounding = context._set_rounding_decision(NEVER_ROUND)
(side, r) = self.__divmod__(other, context=context)
context._set_rounding_decision(rounding)
if r._isnan():
return r
decrease = not side._iseven()
rounding = context._set_rounding_decision(NEVER_ROUND)
side = side.__abs__(context=context)
context._set_rounding_decision(rounding)
s1, s2 = r._sign, comparison._sign
r._sign, comparison._sign = 0, 0
if r > comparison or decrease and r == comparison:
r._sign, comparison._sign = s1, s2
context.prec += 1
if len(side.__add__(Decimal(1), context=context)._int) >= context.prec:
context.prec -= 1
return context._raise_error(DivisionImpossible)[1]
context.prec -= 1
if self._sign == other._sign:
r = r.__sub__(other, context=context)
else:
r = r.__add__(other, context=context)
else:
r._sign, comparison._sign = s1, s2
return r._fix(context)
def __floordiv__(self, other, context=None):
"""self // other"""
return self._divide(other, 2, context)[0]
def __rfloordiv__(self, other, context=None):
"""Swaps self/other and returns __floordiv__."""
other = _convert_other(other)
if other is NotImplemented:
return other
return other.__floordiv__(self, context=context)
def __float__(self):
"""Float representation."""
return float(str(self))
def __int__(self):
"""Converts self to an int, truncating if necessary."""
if self._is_special:
if self._isnan():
context = getcontext()
return context._raise_error(InvalidContext)
elif self._isinfinity():
raise OverflowError, "Cannot convert infinity to long"
if self._exp >= 0:
s = ''.join(map(str, self._int)) + '0'*self._exp
else:
s = ''.join(map(str, self._int))[:self._exp]
if s == '':
s = '0'
sign = '-'*self._sign
return int(sign + s)
def __long__(self):
"""Converts to a long.
Equivalent to long(int(self))
"""
return long(self.__int__())
def _fix(self, context):
"""Round if it is necessary to keep self within prec precision.
Rounds and fixes the exponent. Does not raise on a sNaN.
Arguments:
self - Decimal instance
context - context used.
"""
if self._is_special:
return self
if context is None:
context = getcontext()
prec = context.prec
ans = self._fixexponents(context)
if len(ans._int) > prec:
ans = ans._round(prec, context=context)
ans = ans._fixexponents(context)
return ans
def _fixexponents(self, context):
"""Fix the exponents and return a copy with the exponent in bounds.
Only call if known to not be a special value.
"""
folddown = context._clamp
Emin = context.Emin
ans = self
ans_adjusted = ans.adjusted()
if ans_adjusted < Emin:
Etiny = context.Etiny()
if ans._exp < Etiny:
if not ans:
ans = Decimal(self)
ans._exp = Etiny
context._raise_error(Clamped)
return ans
ans = ans._rescale(Etiny, context=context)
#It isn't zero, and exp < Emin => subnormal
context._raise_error(Subnormal)
if context.flags[Inexact]:
context._raise_error(Underflow)
else:
if ans:
#Only raise subnormal if non-zero.
context._raise_error(Subnormal)
else:
Etop = context.Etop()
if folddown and ans._exp > Etop:
context._raise_error(Clamped)
ans = ans._rescale(Etop, context=context)
else:
Emax = context.Emax
if ans_adjusted > Emax:
if not ans:
ans = Decimal(self)
ans._exp = Emax
context._raise_error(Clamped)
return ans
context._raise_error(Inexact)
context._raise_error(Rounded)
return context._raise_error(Overflow, 'above Emax', ans._sign)
return ans
def _round(self, prec=None, rounding=None, context=None):
"""Returns a rounded version of self.
You can specify the precision or rounding method. Otherwise, the
context determines it.
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
if self._isinfinity():
return Decimal(self)
if context is None:
context = getcontext()
if rounding is None:
rounding = context.rounding
if prec is None:
prec = context.prec
if not self:
if prec <= 0:
dig = (0,)
exp = len(self._int) - prec + self._exp
else:
dig = (0,) * prec
exp = len(self._int) + self._exp - prec
ans = Decimal((self._sign, dig, exp))
context._raise_error(Rounded)
return ans
if prec == 0:
temp = Decimal(self)
temp._int = (0,)+temp._int
prec = 1
elif prec < 0:
exp = self._exp + len(self._int) - prec - 1
temp = Decimal( (self._sign, (0, 1), exp))
prec = 1
else:
temp = Decimal(self)
numdigits = len(temp._int)
if prec == numdigits:
return temp
# See if we need to extend precision
expdiff = prec - numdigits
if expdiff > 0:
tmp = list(temp._int)
tmp.extend([0] * expdiff)
ans = Decimal( (temp._sign, tmp, temp._exp - expdiff))
return ans
#OK, but maybe all the lost digits are 0.
lostdigits = self._int[expdiff:]
if lostdigits == (0,) * len(lostdigits):
ans = Decimal( (temp._sign, temp._int[:prec], temp._exp - expdiff))
#Rounded, but not Inexact
context._raise_error(Rounded)
return ans
# Okay, let's round and lose data
this_function = getattr(temp, self._pick_rounding_function[rounding])
#Now we've got the rounding function
if prec != context.prec:
context = context._shallow_copy()
context.prec = prec
ans = this_function(prec, expdiff, context)
context._raise_error(Rounded)
context._raise_error(Inexact, 'Changed in rounding')
return ans
_pick_rounding_function = {}
def _round_down(self, prec, expdiff, context):
"""Also known as round-towards-0, truncate."""
return Decimal( (self._sign, self._int[:prec], self._exp - expdiff) )
def _round_half_up(self, prec, expdiff, context, tmp = None):
"""Rounds 5 up (away from 0)"""
if tmp is None:
tmp = Decimal( (self._sign,self._int[:prec], self._exp - expdiff))
if self._int[prec] >= 5:
tmp = tmp._increment(round=0, context=context)
if len(tmp._int) > prec:
return Decimal( (tmp._sign, tmp._int[:-1], tmp._exp + 1))
return tmp
def _round_half_even(self, prec, expdiff, context):
"""Round 5 to even, rest to nearest."""
tmp = Decimal( (self._sign, self._int[:prec], self._exp - expdiff))
half = (self._int[prec] == 5)
if half:
for digit in self._int[prec+1:]:
if digit != 0:
half = 0
break
if half:
if self._int[prec-1] & 1 == 0:
return tmp
return self._round_half_up(prec, expdiff, context, tmp)
def _round_half_down(self, prec, expdiff, context):
"""Round 5 down"""
tmp = Decimal( (self._sign, self._int[:prec], self._exp - expdiff))
half = (self._int[prec] == 5)
if half:
for digit in self._int[prec+1:]:
if digit != 0:
half = 0
break
if half:
return tmp
return self._round_half_up(prec, expdiff, context, tmp)
def _round_up(self, prec, expdiff, context):
"""Rounds away from 0."""
tmp = Decimal( (self._sign, self._int[:prec], self._exp - expdiff) )
for digit in self._int[prec:]:
if digit != 0:
tmp = tmp._increment(round=1, context=context)
if len(tmp._int) > prec:
return Decimal( (tmp._sign, tmp._int[:-1], tmp._exp + 1))
else:
return tmp
return tmp
def _round_ceiling(self, prec, expdiff, context):
"""Rounds up (not away from 0 if negative.)"""
if self._sign:
return self._round_down(prec, expdiff, context)
else:
return self._round_up(prec, expdiff, context)
def _round_floor(self, prec, expdiff, context):
"""Rounds down (not towards 0 if negative)"""
if not self._sign:
return self._round_down(prec, expdiff, context)
else:
return self._round_up(prec, expdiff, context)
def __pow__(self, n, modulo = None, context=None):
"""Return self ** n (mod modulo)
If modulo is None (default), don't take it mod modulo.
"""
n = _convert_other(n)
if n is NotImplemented:
return n
if context is None:
context = getcontext()
if self._is_special or n._is_special or n.adjusted() > 8:
#Because the spot << doesn't work with really big exponents
if n._isinfinity() or n.adjusted() > 8:
return context._raise_error(InvalidOperation, 'x ** INF')
ans = self._check_nans(n, context)
if ans:
return ans
if not n._isinteger():
return context._raise_error(InvalidOperation, 'x ** (non-integer)')
if not self and not n:
return context._raise_error(InvalidOperation, '0 ** 0')
if not n:
return Decimal(1)
if self == Decimal(1):
return Decimal(1)
sign = self._sign and not n._iseven()
n = int(n)
if self._isinfinity():
if modulo:
return context._raise_error(InvalidOperation, 'INF % x')
if n > 0:
return Infsign[sign]
return Decimal( (sign, (0,), 0) )
#with ludicrously large exponent, just raise an overflow and return inf.
if not modulo and n > 0 and (self._exp + len(self._int) - 1) * n > context.Emax \
and self:
tmp = Decimal('inf')
tmp._sign = sign
context._raise_error(Rounded)
context._raise_error(Inexact)
context._raise_error(Overflow, 'Big power', sign)
return tmp
elength = len(str(abs(n)))
firstprec = context.prec
if not modulo and firstprec + elength + 1 > DefaultContext.Emax:
return context._raise_error(Overflow, 'Too much precision.', sign)
mul = Decimal(self)
val = Decimal(1)
context = context._shallow_copy()
context.prec = firstprec + elength + 1
if n < 0:
#n is a long now, not Decimal instance
n = -n
mul = Decimal(1).__div__(mul, context=context)
spot = 1
while spot <= n:
spot <<= 1
spot >>= 1
#Spot is the highest power of 2 less than n
while spot:
val = val.__mul__(val, context=context)
if val._isinfinity():
val = Infsign[sign]
break
if spot & n:
val = val.__mul__(mul, context=context)
if modulo is not None:
val = val.__mod__(modulo, context=context)
spot >>= 1
context.prec = firstprec
if context._rounding_decision == ALWAYS_ROUND:
return val._fix(context)
return val
def __rpow__(self, other, context=None):
"""Swaps self/other and returns __pow__."""
other = _convert_other(other)
if other is NotImplemented:
return other
return other.__pow__(self, context=context)
def normalize(self, context=None):
"""Normalize- strip trailing 0s, change anything equal to 0 to 0e0"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
dup = self._fix(context)
if dup._isinfinity():
return dup
if not dup:
return Decimal( (dup._sign, (0,), 0) )
end = len(dup._int)
exp = dup._exp
while dup._int[end-1] == 0:
exp += 1
end -= 1
return Decimal( (dup._sign, dup._int[:end], exp) )
def quantize(self, exp, rounding=None, context=None, watchexp=1):
"""Quantize self so its exponent is the same as that of exp.
Similar to self._rescale(exp._exp) but with error checking.
"""
if self._is_special or exp._is_special:
ans = self._check_nans(exp, context)
if ans:
return ans
if exp._isinfinity() or self._isinfinity():
if exp._isinfinity() and self._isinfinity():
return self #if both are inf, it is OK
if context is None:
context = getcontext()
return context._raise_error(InvalidOperation,
'quantize with one INF')
return self._rescale(exp._exp, rounding, context, watchexp)
def same_quantum(self, other):
"""Test whether self and other have the same exponent.
same as self._exp == other._exp, except NaN == sNaN
"""
if self._is_special or other._is_special:
if self._isnan() or other._isnan():
return self._isnan() and other._isnan() and True
if self._isinfinity() or other._isinfinity():
return self._isinfinity() and other._isinfinity() and True
return self._exp == other._exp
def _rescale(self, exp, rounding=None, context=None, watchexp=1):
"""Rescales so that the exponent is exp.
exp = exp to scale to (an integer)
rounding = rounding version
watchexp: if set (default) an error is returned if exp is greater
than Emax or less than Etiny.
"""
if context is None:
context = getcontext()
if self._is_special:
if self._isinfinity():
return context._raise_error(InvalidOperation, 'rescale with an INF')
ans = self._check_nans(context=context)
if ans:
return ans
if watchexp and (context.Emax < exp or context.Etiny() > exp):
return context._raise_error(InvalidOperation, 'rescale(a, INF)')
if not self:
ans = Decimal(self)
ans._int = (0,)
ans._exp = exp
return ans
diff = self._exp - exp
digits = len(self._int) + diff
if watchexp and digits > context.prec:
return context._raise_error(InvalidOperation, 'Rescale > prec')
tmp = Decimal(self)
tmp._int = (0,) + tmp._int
digits += 1
if digits < 0:
tmp._exp = -digits + tmp._exp
tmp._int = (0,1)
digits = 1
tmp = tmp._round(digits, rounding, context=context)
if tmp._int[0] == 0 and len(tmp._int) > 1:
tmp._int = tmp._int[1:]
tmp._exp = exp
tmp_adjusted = tmp.adjusted()
if tmp and tmp_adjusted < context.Emin:
context._raise_error(Subnormal)
elif tmp and tmp_adjusted > context.Emax:
return context._raise_error(InvalidOperation, 'rescale(a, INF)')
return tmp
def to_integral(self, rounding=None, context=None):
"""Rounds to the nearest integer, without raising inexact, rounded."""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
if self._exp >= 0:
return self
if context is None:
context = getcontext()
flags = context._ignore_flags(Rounded, Inexact)
ans = self._rescale(0, rounding, context=context)
context._regard_flags(flags)
return ans
def sqrt(self, context=None):
"""Return the square root of self.
Uses a converging algorithm (Xn+1 = 0.5*(Xn + self / Xn))
Should quadratically approach the right answer.
"""
if self._is_special:
ans = self._check_nans(context=context)
if ans:
return ans
if self._isinfinity() and self._sign == 0:
return Decimal(self)
if not self:
#exponent = self._exp / 2, using round_down.
#if self._exp < 0:
# exp = (self._exp+1) // 2
#else:
exp = (self._exp) // 2
if self._sign == 1:
#sqrt(-0) = -0
return Decimal( (1, (0,), exp))
else:
return Decimal( (0, (0,), exp))
if context is None:
context = getcontext()
if self._sign == 1:
return context._raise_error(InvalidOperation, 'sqrt(-x), x > 0')
tmp = Decimal(self)
expadd = tmp._exp // 2
if tmp._exp & 1:
tmp._int += (0,)
tmp._exp = 0
else:
tmp._exp = 0
context = context._shallow_copy()
flags = context._ignore_all_flags()
firstprec = context.prec
context.prec = 3
if tmp.adjusted() & 1 == 0:
ans = Decimal( (0, (8,1,9), tmp.adjusted() - 2) )
ans = ans.__add__(tmp.__mul__(Decimal((0, (2,5,9), -2)),
context=context), context=context)
ans._exp -= 1 + tmp.adjusted() // 2
else:
ans = Decimal( (0, (2,5,9), tmp._exp + len(tmp._int)- 3) )
ans = ans.__add__(tmp.__mul__(Decimal((0, (8,1,9), -3)),
context=context), context=context)
ans._exp -= 1 + tmp.adjusted() // 2
#ans is now a linear approximation.
Emax, Emin = context.Emax, context.Emin
context.Emax, context.Emin = DefaultContext.Emax, DefaultContext.Emin
half = Decimal('0.5')
maxp = firstprec + 2
rounding = context._set_rounding(ROUND_HALF_EVEN)
while 1:
context.prec = min(2*context.prec - 2, maxp)
ans = half.__mul__(ans.__add__(tmp.__div__(ans, context=context),
context=context), context=context)
if context.prec == maxp:
break
#round to the answer's precision-- the only error can be 1 ulp.
context.prec = firstprec
prevexp = ans.adjusted()
ans = ans._round(context=context)
#Now, check if the other last digits are better.
context.prec = firstprec + 1
# In case we rounded up another digit and we should actually go lower.
if prevexp != ans.adjusted():
ans._int += (0,)
ans._exp -= 1
lower = ans.__sub__(Decimal((0, (5,), ans._exp-1)), context=context)
context._set_rounding(ROUND_UP)
if lower.__mul__(lower, context=context) > (tmp):
ans = ans.__sub__(Decimal((0, (1,), ans._exp)), context=context)
else:
upper = ans.__add__(Decimal((0, (5,), ans._exp-1)),context=context)
context._set_rounding(ROUND_DOWN)
if upper.__mul__(upper, context=context) < tmp:
ans = ans.__add__(Decimal((0, (1,), ans._exp)),context=context)
ans._exp += expadd
context.prec = firstprec
context.rounding = rounding
ans = ans._fix(context)
rounding = context._set_rounding_decision(NEVER_ROUND)
if not ans.__mul__(ans, context=context) == self:
# Only rounded/inexact if here.
context._regard_flags(flags)
context._raise_error(Rounded)
context._raise_error(Inexact)
else:
#Exact answer, so let's set the exponent right.
#if self._exp < 0:
# exp = (self._exp +1)// 2
#else:
exp = self._exp // 2
context.prec += ans._exp - exp
ans = ans._rescale(exp, context=context)
context.prec = firstprec
context._regard_flags(flags)
context.Emax, context.Emin = Emax, Emin
return ans._fix(context)
def max(self, other, context=None):
"""Returns the larger value.
like max(self, other) except if one is not a number, returns
NaN (and signals if one is sNaN). Also rounds.
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
# if one operand is a quiet NaN and the other is number, then the
# number is always returned
sn = self._isnan()
on = other._isnan()
if sn or on:
if on == 1 and sn != 2:
return self
if sn == 1 and on != 2:
return other
return self._check_nans(other, context)
ans = self
c = self.__cmp__(other)
if c == 0:
# if both operands are finite and equal in numerical value
# then an ordering is applied:
#
# if the signs differ then max returns the operand with the
# positive sign and min returns the operand with the negative sign
#
# if the signs are the same then the exponent is used to select
# the result.
if self._sign != other._sign:
if self._sign:
ans = other
elif self._exp < other._exp and not self._sign:
ans = other
elif self._exp > other._exp and self._sign:
ans = other
elif c == -1:
ans = other
if context is None:
context = getcontext()
if context._rounding_decision == ALWAYS_ROUND:
return ans._fix(context)
return ans
def min(self, other, context=None):
"""Returns the smaller value.
like min(self, other) except if one is not a number, returns
NaN (and signals if one is sNaN). Also rounds.
"""
other = _convert_other(other)
if other is NotImplemented:
return other
if self._is_special or other._is_special:
# if one operand is a quiet NaN and the other is number, then the
# number is always returned
sn = self._isnan()
on = other._isnan()
if sn or on:
if on == 1 and sn != 2:
return self
if sn == 1 and on != 2:
return other
return self._check_nans(other, context)
ans = self
c = self.__cmp__(other)
if c == 0:
# if both operands are finite and equal in numerical value
# then an ordering is applied:
#
# if the signs differ then max returns the operand with the
# positive sign and min returns the operand with the negative sign
#
# if the signs are the same then the exponent is used to select
# the result.
if self._sign != other._sign:
if other._sign:
ans = other
elif self._exp > other._exp and not self._sign:
ans = other
elif self._exp < other._exp and self._sign:
ans = other
elif c == 1:
ans = other
if context is None:
context = getcontext()
if context._rounding_decision == ALWAYS_ROUND:
return ans._fix(context)
return ans
def _isinteger(self):
"""Returns whether self is an integer"""
if self._exp >= 0:
return True
rest = self._int[self._exp:]
return rest == (0,)*len(rest)
def _iseven(self):
"""Returns 1 if self is even. Assumes self is an integer."""
if self._exp > 0:
return 1
return self._int[-1+self._exp] & 1 == 0
def adjusted(self):
"""Return the adjusted exponent of self"""
try:
return self._exp + len(self._int) - 1
#If NaN or Infinity, self._exp is string
except TypeError:
return 0
# support for pickling, copy, and deepcopy
def __reduce__(self):
return (self.__class__, (str(self),))
def __copy__(self):
if type(self) == Decimal:
return self # I'm immutable; therefore I am my own clone
return self.__class__(str(self))
def __deepcopy__(self, memo):
if type(self) == Decimal:
return self # My components are also immutable
return self.__class__(str(self))
##### Context class ###########################################
# get rounding method function:
rounding_functions = [name for name in Decimal.__dict__.keys() if name.startswith('_round_')]
for name in rounding_functions:
#name is like _round_half_even, goes to the global ROUND_HALF_EVEN value.
globalname = name[1:].upper()
val = globals()[globalname]
Decimal._pick_rounding_function[val] = name
del name, val, globalname, rounding_functions
class WithStatementContext(object):
"""Helper class to simplify Context management.
Sample usage:
with decimal.ExtendedContext:
s = ...
return +s # Convert result to normal precision
with decimal.getcontext() as ctx:
ctx.prec += 2
s = ...
return +s
"""
def __init__(self, new_context):
self.new_context = new_context
def __enter__(self):
self.saved_context = getcontext()
setcontext(self.new_context)
return self.new_context
def __exit__(self, t, v, tb):
setcontext(self.saved_context)
class Context(object):
"""Contains the context for a Decimal instance.
Contains:
prec - precision (for use in rounding, division, square roots..)
rounding - rounding type. (how you round)
_rounding_decision - ALWAYS_ROUND, NEVER_ROUND -- do you round?
traps - If traps[exception] = 1, then the exception is
raised when it is caused. Otherwise, a value is
substituted in.
flags - When an exception is caused, flags[exception] is incremented.
(Whether or not the trap_enabler is set)
Should be reset by user of Decimal instance.
Emin - Minimum exponent
Emax - Maximum exponent
capitals - If 1, 1*10^1 is printed as 1E+1.
If 0, printed as 1e1
_clamp - If 1, change exponents if too high (Default 0)
"""
def __init__(self, prec=None, rounding=None,
traps=None, flags=None,
_rounding_decision=None,
Emin=None, Emax=None,
capitals=None, _clamp=0,
_ignored_flags=None):
if flags is None:
flags = []
if _ignored_flags is None:
_ignored_flags = []
if not isinstance(flags, dict):
flags = dict([(s,s in flags) for s in _signals])
del s
if traps is not None and not isinstance(traps, dict):
traps = dict([(s,s in traps) for s in _signals])
del s
for name, val in locals().items():
if val is None:
setattr(self, name, _copy.copy(getattr(DefaultContext, name)))
else:
setattr(self, name, val)
del self.self
def __repr__(self):
"""Show the current context."""
s = []
s.append('Context(prec=%(prec)d, rounding=%(rounding)s, Emin=%(Emin)d, Emax=%(Emax)d, capitals=%(capitals)d' % vars(self))
s.append('flags=[' + ', '.join([f.__name__ for f, v in self.flags.items() if v]) + ']')
s.append('traps=[' + ', '.join([t.__name__ for t, v in self.traps.items() if v]) + ']')
return ', '.join(s) + ')'
def context_manager(self):
return WithStatementContext(self.copy())
def clear_flags(self):
"""Reset all flags to zero"""
for flag in self.flags:
self.flags[flag] = 0
def _shallow_copy(self):
"""Returns a shallow copy from self."""
nc = Context(self.prec, self.rounding, self.traps, self.flags,
self._rounding_decision, self.Emin, self.Emax,
self.capitals, self._clamp, self._ignored_flags)
return nc
def copy(self):
"""Returns a deep copy from self."""
nc = Context(self.prec, self.rounding, self.traps.copy(), self.flags.copy(),
self._rounding_decision, self.Emin, self.Emax,
self.capitals, self._clamp, self._ignored_flags)
return nc
__copy__ = copy
def _raise_error(self, condition, explanation = None, *args):
"""Handles an error
If the flag is in _ignored_flags, returns the default response.
Otherwise, it increments the flag, then, if the corresponding
trap_enabler is set, it reaises the exception. Otherwise, it returns
the default value after incrementing the flag.
"""
error = _condition_map.get(condition, condition)
if error in self._ignored_flags:
#Don't touch the flag
return error().handle(self, *args)
self.flags[error] += 1
if not self.traps[error]:
#The errors define how to handle themselves.
return condition().handle(self, *args)
# Errors should only be risked on copies of the context
#self._ignored_flags = []
raise error, explanation
def _ignore_all_flags(self):
"""Ignore all flags, if they are raised"""
return self._ignore_flags(*_signals)
def _ignore_flags(self, *flags):
"""Ignore the flags, if they are raised"""
# Do not mutate-- This way, copies of a context leave the original
# alone.
self._ignored_flags = (self._ignored_flags + list(flags))
return list(flags)
def _regard_flags(self, *flags):
"""Stop ignoring the flags, if they are raised"""
if flags and isinstance(flags[0], (tuple,list)):
flags = flags[0]
for flag in flags:
self._ignored_flags.remove(flag)
def __hash__(self):
"""A Context cannot be hashed."""
# We inherit object.__hash__, so we must deny this explicitly
raise TypeError, "Cannot hash a Context."
def Etiny(self):
"""Returns Etiny (= Emin - prec + 1)"""
return int(self.Emin - self.prec + 1)
def Etop(self):
"""Returns maximum exponent (= Emax - prec + 1)"""
return int(self.Emax - self.prec + 1)
def _set_rounding_decision(self, type):
"""Sets the rounding decision.
Sets the rounding decision, and returns the current (previous)
rounding decision. Often used like:
context = context._shallow_copy()
# That so you don't change the calling context
# if an error occurs in the middle (say DivisionImpossible is raised).
rounding = context._set_rounding_decision(NEVER_ROUND)
instance = instance / Decimal(2)
context._set_rounding_decision(rounding)
This will make it not round for that operation.
"""
rounding = self._rounding_decision
self._rounding_decision = type
return rounding
def _set_rounding(self, type):
"""Sets the rounding type.
Sets the rounding type, and returns the current (previous)
rounding type. Often used like:
context = context.copy()
# so you don't change the calling context
# if an error occurs in the middle.
rounding = context._set_rounding(ROUND_UP)
val = self.__sub__(other, context=context)
context._set_rounding(rounding)
This will make it round up for that operation.
"""
rounding = self.rounding
self.rounding= type
return rounding
def create_decimal(self, num='0'):
"""Creates a new Decimal instance but using self as context."""
d = Decimal(num, context=self)
return d._fix(self)
#Methods
def abs(self, a):
"""Returns the absolute value of the operand.
If the operand is negative, the result is the same as using the minus
operation on the operand. Otherwise, the result is the same as using
the plus operation on the operand.
>>> ExtendedContext.abs(Decimal('2.1'))
Decimal("2.1")
>>> ExtendedContext.abs(Decimal('-100'))
Decimal("100")
>>> ExtendedContext.abs(Decimal('101.5'))
Decimal("101.5")
>>> ExtendedContext.abs(Decimal('-101.5'))
Decimal("101.5")
"""
return a.__abs__(context=self)
def add(self, a, b):
"""Return the sum of the two operands.
>>> ExtendedContext.add(Decimal('12'), Decimal('7.00'))
Decimal("19.00")
>>> ExtendedContext.add(Decimal('1E+2'), Decimal('1.01E+4'))
Decimal("1.02E+4")
"""
return a.__add__(b, context=self)
def _apply(self, a):
return str(a._fix(self))
def compare(self, a, b):
"""Compares values numerically.
If the signs of the operands differ, a value representing each operand
('-1' if the operand is less than zero, '0' if the operand is zero or
negative zero, or '1' if the operand is greater than zero) is used in
place of that operand for the comparison instead of the actual
operand.
The comparison is then effected by subtracting the second operand from
the first and then returning a value according to the result of the
subtraction: '-1' if the result is less than zero, '0' if the result is
zero or negative zero, or '1' if the result is greater than zero.
>>> ExtendedContext.compare(Decimal('2.1'), Decimal('3'))
Decimal("-1")
>>> ExtendedContext.compare(Decimal('2.1'), Decimal('2.1'))
Decimal("0")
>>> ExtendedContext.compare(Decimal('2.1'), Decimal('2.10'))
Decimal("0")
>>> ExtendedContext.compare(Decimal('3'), Decimal('2.1'))
Decimal("1")
>>> ExtendedContext.compare(Decimal('2.1'), Decimal('-3'))
Decimal("1")
>>> ExtendedContext.compare(Decimal('-3'), Decimal('2.1'))
Decimal("-1")
"""
return a.compare(b, context=self)
def divide(self, a, b):
"""Decimal division in a specified context.
>>> ExtendedContext.divide(Decimal('1'), Decimal('3'))
Decimal("0.333333333")
>>> ExtendedContext.divide(Decimal('2'), Decimal('3'))
Decimal("0.666666667")
>>> ExtendedContext.divide(Decimal('5'), Decimal('2'))
Decimal("2.5")
>>> ExtendedContext.divide(Decimal('1'), Decimal('10'))
Decimal("0.1")
>>> ExtendedContext.divide(Decimal('12'), Decimal('12'))
Decimal("1")
>>> ExtendedContext.divide(Decimal('8.00'), Decimal('2'))
Decimal("4.00")
>>> ExtendedContext.divide(Decimal('2.400'), Decimal('2.0'))
Decimal("1.20")
>>> ExtendedContext.divide(Decimal('1000'), Decimal('100'))
Decimal("10")
>>> ExtendedContext.divide(Decimal('1000'), Decimal('1'))
Decimal("1000")
>>> ExtendedContext.divide(Decimal('2.40E+6'), Decimal('2'))
Decimal("1.20E+6")
"""
return a.__div__(b, context=self)
def divide_int(self, a, b):
"""Divides two numbers and returns the integer part of the result.
>>> ExtendedContext.divide_int(Decimal('2'), Decimal('3'))
Decimal("0")
>>> ExtendedContext.divide_int(Decimal('10'), Decimal('3'))
Decimal("3")
>>> ExtendedContext.divide_int(Decimal('1'), Decimal('0.3'))
Decimal("3")
"""
return a.__floordiv__(b, context=self)
def divmod(self, a, b):
return a.__divmod__(b, context=self)
def max(self, a,b):
"""max compares two values numerically and returns the maximum.
If either operand is a NaN then the general rules apply.
Otherwise, the operands are compared as as though by the compare
operation. If they are numerically equal then the left-hand operand
is chosen as the result. Otherwise the maximum (closer to positive
infinity) of the two operands is chosen as the result.
>>> ExtendedContext.max(Decimal('3'), Decimal('2'))
Decimal("3")
>>> ExtendedContext.max(Decimal('-10'), Decimal('3'))
Decimal("3")
>>> ExtendedContext.max(Decimal('1.0'), Decimal('1'))
Decimal("1")
>>> ExtendedContext.max(Decimal('7'), Decimal('NaN'))
Decimal("7")
"""
return a.max(b, context=self)
def min(self, a,b):
"""min compares two values numerically and returns the minimum.
If either operand is a NaN then the general rules apply.
Otherwise, the operands are compared as as though by the compare
operation. If they are numerically equal then the left-hand operand
is chosen as the result. Otherwise the minimum (closer to negative
infinity) of the two operands is chosen as the result.
>>> ExtendedContext.min(Decimal('3'), Decimal('2'))
Decimal("2")
>>> ExtendedContext.min(Decimal('-10'), Decimal('3'))
Decimal("-10")
>>> ExtendedContext.min(Decimal('1.0'), Decimal('1'))
Decimal("1.0")
>>> ExtendedContext.min(Decimal('7'), Decimal('NaN'))
Decimal("7")
"""
return a.min(b, context=self)
def minus(self, a):
"""Minus corresponds to unary prefix minus in Python.
The operation is evaluated using the same rules as subtract; the
operation minus(a) is calculated as subtract('0', a) where the '0'
has the same exponent as the operand.
>>> ExtendedContext.minus(Decimal('1.3'))
Decimal("-1.3")
>>> ExtendedContext.minus(Decimal('-1.3'))
Decimal("1.3")
"""
return a.__neg__(context=self)
def multiply(self, a, b):
"""multiply multiplies two operands.
If either operand is a special value then the general rules apply.
Otherwise, the operands are multiplied together ('long multiplication'),
resulting in a number which may be as long as the sum of the lengths
of the two operands.
>>> ExtendedContext.multiply(Decimal('1.20'), Decimal('3'))
Decimal("3.60")
>>> ExtendedContext.multiply(Decimal('7'), Decimal('3'))
Decimal("21")
>>> ExtendedContext.multiply(Decimal('0.9'), Decimal('0.8'))
Decimal("0.72")
>>> ExtendedContext.multiply(Decimal('0.9'), Decimal('-0'))
Decimal("-0.0")
>>> ExtendedContext.multiply(Decimal('654321'), Decimal('654321'))
Decimal("4.28135971E+11")
"""
return a.__mul__(b, context=self)
def normalize(self, a):
"""normalize reduces an operand to its simplest form.
Essentially a plus operation with all trailing zeros removed from the
result.
>>> ExtendedContext.normalize(Decimal('2.1'))
Decimal("2.1")
>>> ExtendedContext.normalize(Decimal('-2.0'))
Decimal("-2")
>>> ExtendedContext.normalize(Decimal('1.200'))
Decimal("1.2")
>>> ExtendedContext.normalize(Decimal('-120'))
Decimal("-1.2E+2")
>>> ExtendedContext.normalize(Decimal('120.00'))
Decimal("1.2E+2")
>>> ExtendedContext.normalize(Decimal('0.00'))
Decimal("0")
"""
return a.normalize(context=self)
def plus(self, a):
"""Plus corresponds to unary prefix plus in Python.
The operation is evaluated using the same rules as add; the
operation plus(a) is calculated as add('0', a) where the '0'
has the same exponent as the operand.
>>> ExtendedContext.plus(Decimal('1.3'))
Decimal("1.3")
>>> ExtendedContext.plus(Decimal('-1.3'))
Decimal("-1.3")
"""
return a.__pos__(context=self)
def power(self, a, b, modulo=None):
"""Raises a to the power of b, to modulo if given.
The right-hand operand must be a whole number whose integer part (after
any exponent has been applied) has no more than 9 digits and whose
fractional part (if any) is all zeros before any rounding. The operand
may be positive, negative, or zero; if negative, the absolute value of
the power is used, and the left-hand operand is inverted (divided into
1) before use.
If the increased precision needed for the intermediate calculations
exceeds the capabilities of the implementation then an Invalid operation
condition is raised.
If, when raising to a negative power, an underflow occurs during the
division into 1, the operation is not halted at that point but
continues.
>>> ExtendedContext.power(Decimal('2'), Decimal('3'))
Decimal("8")
>>> ExtendedContext.power(Decimal('2'), Decimal('-3'))
Decimal("0.125")
>>> ExtendedContext.power(Decimal('1.7'), Decimal('8'))
Decimal("69.7575744")
>>> ExtendedContext.power(Decimal('Infinity'), Decimal('-2'))
Decimal("0")
>>> ExtendedContext.power(Decimal('Infinity'), Decimal('-1'))
Decimal("0")
>>> ExtendedContext.power(Decimal('Infinity'), Decimal('0'))
Decimal("1")
>>> ExtendedContext.power(Decimal('Infinity'), Decimal('1'))
Decimal("Infinity")
>>> ExtendedContext.power(Decimal('Infinity'), Decimal('2'))
Decimal("Infinity")
>>> ExtendedContext.power(Decimal('-Infinity'), Decimal('-2'))
Decimal("0")
>>> ExtendedContext.power(Decimal('-Infinity'), Decimal('-1'))
Decimal("-0")
>>> ExtendedContext.power(Decimal('-Infinity'), Decimal('0'))
Decimal("1")
>>> ExtendedContext.power(Decimal('-Infinity'), Decimal('1'))
Decimal("-Infinity")
>>> ExtendedContext.power(Decimal('-Infinity'), Decimal('2'))
Decimal("Infinity")
>>> ExtendedContext.power(Decimal('0'), Decimal('0'))
Decimal("NaN")
"""
return a.__pow__(b, modulo, context=self)
def quantize(self, a, b):
"""Returns a value equal to 'a' (rounded) and having the exponent of 'b'.
The coefficient of the result is derived from that of the left-hand
operand. It may be rounded using the current rounding setting (if the
exponent is being increased), multiplied by a positive power of ten (if
the exponent is being decreased), or is unchanged (if the exponent is
already equal to that of the right-hand operand).
Unlike other operations, if the length of the coefficient after the
quantize operation would be greater than precision then an Invalid
operation condition is raised. This guarantees that, unless there is an
error condition, the exponent of the result of a quantize is always
equal to that of the right-hand operand.
Also unlike other operations, quantize will never raise Underflow, even
if the result is subnormal and inexact.
>>> ExtendedContext.quantize(Decimal('2.17'), Decimal('0.001'))
Decimal("2.170")
>>> ExtendedContext.quantize(Decimal('2.17'), Decimal('0.01'))
Decimal("2.17")
>>> ExtendedContext.quantize(Decimal('2.17'), Decimal('0.1'))
Decimal("2.2")
>>> ExtendedContext.quantize(Decimal('2.17'), Decimal('1e+0'))
Decimal("2")
>>> ExtendedContext.quantize(Decimal('2.17'), Decimal('1e+1'))
Decimal("0E+1")
>>> ExtendedContext.quantize(Decimal('-Inf'), Decimal('Infinity'))
Decimal("-Infinity")
>>> ExtendedContext.quantize(Decimal('2'), Decimal('Infinity'))
Decimal("NaN")
>>> ExtendedContext.quantize(Decimal('-0.1'), Decimal('1'))
Decimal("-0")
>>> ExtendedContext.quantize(Decimal('-0'), Decimal('1e+5'))
Decimal("-0E+5")
>>> ExtendedContext.quantize(Decimal('+35236450.6'), Decimal('1e-2'))
Decimal("NaN")
>>> ExtendedContext.quantize(Decimal('-35236450.6'), Decimal('1e-2'))
Decimal("NaN")
>>> ExtendedContext.quantize(Decimal('217'), Decimal('1e-1'))
Decimal("217.0")
>>> ExtendedContext.quantize(Decimal('217'), Decimal('1e-0'))
Decimal("217")
>>> ExtendedContext.quantize(Decimal('217'), Decimal('1e+1'))
Decimal("2.2E+2")
>>> ExtendedContext.quantize(Decimal('217'), Decimal('1e+2'))
Decimal("2E+2")
"""
return a.quantize(b, context=self)
def remainder(self, a, b):
"""Returns the remainder from integer division.
The result is the residue of the dividend after the operation of
calculating integer division as described for divide-integer, rounded to
precision digits if necessary. The sign of the result, if non-zero, is
the same as that of the original dividend.
This operation will fail under the same conditions as integer division
(that is, if integer division on the same two operands would fail, the
remainder cannot be calculated).
>>> ExtendedContext.remainder(Decimal('2.1'), Decimal('3'))
Decimal("2.1")
>>> ExtendedContext.remainder(Decimal('10'), Decimal('3'))
Decimal("1")
>>> ExtendedContext.remainder(Decimal('-10'), Decimal('3'))
Decimal("-1")
>>> ExtendedContext.remainder(Decimal('10.2'), Decimal('1'))
Decimal("0.2")
>>> ExtendedContext.remainder(Decimal('10'), Decimal('0.3'))
Decimal("0.1")
>>> ExtendedContext.remainder(Decimal('3.6'), Decimal('1.3'))
Decimal("1.0")
"""
return a.__mod__(b, context=self)
def remainder_near(self, a, b):
"""Returns to be "a - b * n", where n is the integer nearest the exact
value of "x / b" (if two integers are equally near then the even one
is chosen). If the result is equal to 0 then its sign will be the
sign of a.
This operation will fail under the same conditions as integer division
(that is, if integer division on the same two operands would fail, the
remainder cannot be calculated).
>>> ExtendedContext.remainder_near(Decimal('2.1'), Decimal('3'))
Decimal("-0.9")
>>> ExtendedContext.remainder_near(Decimal('10'), Decimal('6'))
Decimal("-2")
>>> ExtendedContext.remainder_near(Decimal('10'), Decimal('3'))
Decimal("1")
>>> ExtendedContext.remainder_near(Decimal('-10'), Decimal('3'))
Decimal("-1")
>>> ExtendedContext.remainder_near(Decimal('10.2'), Decimal('1'))
Decimal("0.2")
>>> ExtendedContext.remainder_near(Decimal('10'), Decimal('0.3'))
Decimal("0.1")
>>> ExtendedContext.remainder_near(Decimal('3.6'), Decimal('1.3'))
Decimal("-0.3")
"""
return a.remainder_near(b, context=self)
def same_quantum(self, a, b):
"""Returns True if the two operands have the same exponent.
The result is never affected by either the sign or the coefficient of
either operand.
>>> ExtendedContext.same_quantum(Decimal('2.17'), Decimal('0.001'))
False
>>> ExtendedContext.same_quantum(Decimal('2.17'), Decimal('0.01'))
True
>>> ExtendedContext.same_quantum(Decimal('2.17'), Decimal('1'))
False
>>> ExtendedContext.same_quantum(Decimal('Inf'), Decimal('-Inf'))
True
"""
return a.same_quantum(b)
def sqrt(self, a):
"""Returns the square root of a non-negative number to context precision.
If the result must be inexact, it is rounded using the round-half-even
algorithm.
>>> ExtendedContext.sqrt(Decimal('0'))
Decimal("0")
>>> ExtendedContext.sqrt(Decimal('-0'))
Decimal("-0")
>>> ExtendedContext.sqrt(Decimal('0.39'))
Decimal("0.624499800")
>>> ExtendedContext.sqrt(Decimal('100'))
Decimal("10")
>>> ExtendedContext.sqrt(Decimal('1'))
Decimal("1")
>>> ExtendedContext.sqrt(Decimal('1.0'))
Decimal("1.0")
>>> ExtendedContext.sqrt(Decimal('1.00'))
Decimal("1.0")
>>> ExtendedContext.sqrt(Decimal('7'))
Decimal("2.64575131")
>>> ExtendedContext.sqrt(Decimal('10'))
Decimal("3.16227766")
>>> ExtendedContext.prec
9
"""
return a.sqrt(context=self)
def subtract(self, a, b):
"""Return the difference between the two operands.
>>> ExtendedContext.subtract(Decimal('1.3'), Decimal('1.07'))
Decimal("0.23")
>>> ExtendedContext.subtract(Decimal('1.3'), Decimal('1.30'))
Decimal("0.00")
>>> ExtendedContext.subtract(Decimal('1.3'), Decimal('2.07'))
Decimal("-0.77")
"""
return a.__sub__(b, context=self)
def to_eng_string(self, a):
"""Converts a number to a string, using scientific notation.
The operation is not affected by the context.
"""
return a.to_eng_string(context=self)
def to_sci_string(self, a):
"""Converts a number to a string, using scientific notation.
The operation is not affected by the context.
"""
return a.__str__(context=self)
def to_integral(self, a):
"""Rounds to an integer.
When the operand has a negative exponent, the result is the same
as using the quantize() operation using the given operand as the
left-hand-operand, 1E+0 as the right-hand-operand, and the precision
of the operand as the precision setting, except that no flags will
be set. The rounding mode is taken from the context.
>>> ExtendedContext.to_integral(Decimal('2.1'))
Decimal("2")
>>> ExtendedContext.to_integral(Decimal('100'))
Decimal("100")
>>> ExtendedContext.to_integral(Decimal('100.0'))
Decimal("100")
>>> ExtendedContext.to_integral(Decimal('101.5'))
Decimal("102")
>>> ExtendedContext.to_integral(Decimal('-101.5'))
Decimal("-102")
>>> ExtendedContext.to_integral(Decimal('10E+5'))
Decimal("1.0E+6")
>>> ExtendedContext.to_integral(Decimal('7.89E+77'))
Decimal("7.89E+77")
>>> ExtendedContext.to_integral(Decimal('-Inf'))
Decimal("-Infinity")
"""
return a.to_integral(context=self)
class _WorkRep(object):
__slots__ = ('sign','int','exp')
# sign: 0 or 1
# int: int or long
# exp: None, int, or string
def __init__(self, value=None):
if value is None:
self.sign = None
self.int = 0
self.exp = None
elif isinstance(value, Decimal):
self.sign = value._sign
cum = 0
for digit in value._int:
cum = cum * 10 + digit
self.int = cum
self.exp = value._exp
else:
# assert isinstance(value, tuple)
self.sign = value[0]
self.int = value[1]
self.exp = value[2]
def __repr__(self):
return "(%r, %r, %r)" % (self.sign, self.int, self.exp)
__str__ = __repr__
def _normalize(op1, op2, shouldround = 0, prec = 0):
"""Normalizes op1, op2 to have the same exp and length of coefficient.
Done during addition.
"""
# Yes, the exponent is a long, but the difference between exponents
# must be an int-- otherwise you'd get a big memory problem.
numdigits = int(op1.exp - op2.exp)
if numdigits < 0:
numdigits = -numdigits
tmp = op2
other = op1
else:
tmp = op1
other = op2
if shouldround and numdigits > prec + 1:
# Big difference in exponents - check the adjusted exponents
tmp_len = len(str(tmp.int))
other_len = len(str(other.int))
if numdigits > (other_len + prec + 1 - tmp_len):
# If the difference in adjusted exps is > prec+1, we know
# other is insignificant, so might as well put a 1 after the precision.
# (since this is only for addition.) Also stops use of massive longs.
extend = prec + 2 - tmp_len
if extend <= 0:
extend = 1
tmp.int *= 10 ** extend
tmp.exp -= extend
other.int = 1
other.exp = tmp.exp
return op1, op2
tmp.int *= 10 ** numdigits
tmp.exp -= numdigits
return op1, op2
def _adjust_coefficients(op1, op2):
"""Adjust op1, op2 so that op2.int * 10 > op1.int >= op2.int.
Returns the adjusted op1, op2 as well as the change in op1.exp-op2.exp.
Used on _WorkRep instances during division.
"""
adjust = 0
#If op1 is smaller, make it larger
while op2.int > op1.int:
op1.int *= 10
op1.exp -= 1
adjust += 1
#If op2 is too small, make it larger
while op1.int >= (10 * op2.int):
op2.int *= 10
op2.exp -= 1
adjust -= 1
return op1, op2, adjust
##### Helper Functions ########################################
def _convert_other(other):
"""Convert other to Decimal.
Verifies that it's ok to use in an implicit construction.
"""
if isinstance(other, Decimal):
return other
if isinstance(other, (int, long)):
return Decimal(other)
return NotImplemented
_infinity_map = {
'inf' : 1,
'infinity' : 1,
'+inf' : 1,
'+infinity' : 1,
'-inf' : -1,
'-infinity' : -1
}
def _isinfinity(num):
"""Determines whether a string or float is infinity.
+1 for negative infinity; 0 for finite ; +1 for positive infinity
"""
num = str(num).lower()
return _infinity_map.get(num, 0)
def _isnan(num):
"""Determines whether a string or float is NaN
(1, sign, diagnostic info as string) => NaN
(2, sign, diagnostic info as string) => sNaN
0 => not a NaN
"""
num = str(num).lower()
if not num:
return 0
#get the sign, get rid of trailing [+-]
sign = 0
if num[0] == '+':
num = num[1:]
elif num[0] == '-': #elif avoids '+-nan'
num = num[1:]
sign = 1
if num.startswith('nan'):
if len(num) > 3 and not num[3:].isdigit(): #diagnostic info
return 0
return (1, sign, num[3:].lstrip('0'))
if num.startswith('snan'):
if len(num) > 4 and not num[4:].isdigit():
return 0
return (2, sign, num[4:].lstrip('0'))
return 0
##### Setup Specific Contexts ################################
# The default context prototype used by Context()
# Is mutable, so that new contexts can have different default values
DefaultContext = Context(
prec=28, rounding=ROUND_HALF_EVEN,
traps=[DivisionByZero, Overflow, InvalidOperation],
flags=[],
_rounding_decision=ALWAYS_ROUND,
Emax=999999999,
Emin=-999999999,
capitals=1
)
# Pre-made alternate contexts offered by the specification
# Don't change these; the user should be able to select these
# contexts and be able to reproduce results from other implementations
# of the spec.
BasicContext = Context(
prec=9, rounding=ROUND_HALF_UP,
traps=[DivisionByZero, Overflow, InvalidOperation, Clamped, Underflow],
flags=[],
)
ExtendedContext = Context(
prec=9, rounding=ROUND_HALF_EVEN,
traps=[],
flags=[],
)
##### Useful Constants (internal use only) ####################
#Reusable defaults
Inf = Decimal('Inf')
negInf = Decimal('-Inf')
#Infsign[sign] is infinity w/ that sign
Infsign = (Inf, negInf)
NaN = Decimal('NaN')
##### crud for parsing strings #################################
import re
# There's an optional sign at the start, and an optional exponent
# at the end. The exponent has an optional sign and at least one
# digit. In between, must have either at least one digit followed
# by an optional fraction, or a decimal point followed by at least
# one digit. Yuck.
_parser = re.compile(r"""
# \s*
(?P<sign>[-+])?
(
(?P<int>\d+) (\. (?P<frac>\d*))?
|
\. (?P<onlyfrac>\d+)
)
([eE](?P<exp>[-+]? \d+))?
# \s*
$
""", re.VERBOSE).match #Uncomment the \s* to allow leading or trailing spaces.
del re
# return sign, n, p s.t. float string value == -1**sign * n * 10**p exactly
def _string2exact(s):
m = _parser(s)
if m is None:
raise ValueError("invalid literal for Decimal: %r" % s)
if m.group('sign') == "-":
sign = 1
else:
sign = 0
exp = m.group('exp')
if exp is None:
exp = 0
else:
exp = int(exp)
intpart = m.group('int')
if intpart is None:
intpart = ""
fracpart = m.group('onlyfrac')
else:
fracpart = m.group('frac')
if fracpart is None:
fracpart = ""
exp -= len(fracpart)
mantissa = intpart + fracpart
tmp = map(int, mantissa)
backup = tmp
while tmp and tmp[0] == 0:
del tmp[0]
# It's a zero
if not tmp:
if backup:
return (sign, tuple(backup), exp)
return (sign, (0,), exp)
mantissa = tuple(tmp)
return (sign, mantissa, exp)
if __name__ == '__main__':
import doctest, sys
doctest.testmod(sys.modules[__name__])
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