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gh-67790: Support float-style formatting for Fraction instances (#100161)
This PR adds support for float-style formatting for `Fraction` objects: it supports the `"e"`, `"E"`, `"f"`, `"F"`, `"g"`, `"G"` and `"%"` presentation types, and all the various bells and whistles of the formatting mini-language for those presentation types. The behaviour almost exactly matches that of `float`, but the implementation works with the exact `Fraction` value and does not do an intermediate conversion to `float`, and so avoids loss of precision or issues with numbers that are outside the dynamic range of the `float` type.
Note that the `"n"` presentation type is _not_ supported. That support could be added later if people have a need for it.
There's one corner-case where the behaviour differs from that of float: for the `float` type, if explicit alignment is specified with a fill character of `'0'` and alignment type `'='`, then thousands separators (if specified) are inserted into the padding string:
```python
>>> format(3.14, '0=11,.2f')
'0,000,003.14'
```
The exact same effect can be achieved by using the `'0'` flag:
```python
>>> format(3.14, '011,.2f')
'0,000,003.14'
```
For `Fraction`, only the `'0'` flag has the above behaviour with respect to thousands separators: there's no special-casing of the particular `'0='` fill-character/alignment combination. Instead, we treat the fill character `'0'` just like any other:
```python
>>> format(Fraction('3.14'), '0=11,.2f')
'00000003.14'
>>> format(Fraction('3.14'), '011,.2f')
'0,000,003.14'
```
The `Fraction` formatter is also stricter about combining these two things: it's not permitted to use both the `'0'` flag _and_ explicit alignment, on the basis that we should refuse the temptation to guess in the face of ambiguity. `float` is less picky:
```python
>>> format(3.14, '0<011,.2f')
'3.140000000'
>>> format(Fraction('3.14'), '0<011,.2f')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/mdickinson/Repositories/python/cpython/Lib/fractions.py", line 414, in __format__
raise ValueError(
ValueError: Invalid format specifier '0<011,.2f' for object of type 'Fraction'; can't use explicit alignment when zero-padding
```
This commit is contained in:
Mark Dickinson
GitHub
parent
b53bad6dd0
commit
3e09f3152e
5 changed files with 618 additions and 0 deletions
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@ -101,6 +101,11 @@ another rational number, or from a string.
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.. versionchanged:: 3.12
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Space is allowed around the slash for string inputs: ``Fraction('2 / 3')``.
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.. versionchanged:: 3.12
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:class:`Fraction` instances now support float-style formatting, with
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presentation types ``"e"``, ``"E"``, ``"f"``, ``"F"``, ``"g"``, ``"G"``
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and ``"%""``.
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.. attribute:: numerator
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Numerator of the Fraction in lowest term.
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@ -193,6 +198,29 @@ another rational number, or from a string.
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``ndigits`` is negative), again rounding half toward even. This
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method can also be accessed through the :func:`round` function.
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.. method:: __format__(format_spec, /)
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Provides support for float-style formatting of :class:`Fraction`
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instances via the :meth:`str.format` method, the :func:`format` built-in
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function, or :ref:`Formatted string literals <f-strings>`. The
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presentation types ``"e"``, ``"E"``, ``"f"``, ``"F"``, ``"g"``, ``"G"``
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and ``"%"`` are supported. For these presentation types, formatting for a
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:class:`Fraction` object ``x`` follows the rules outlined for
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the :class:`float` type in the :ref:`formatspec` section.
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Here are some examples::
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>>> from fractions import Fraction
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>>> format(Fraction(1, 7), '.40g')
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'0.1428571428571428571428571428571428571429'
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>>> format(Fraction('1234567.855'), '_.2f')
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'1_234_567.86'
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>>> f"{Fraction(355, 113):*>20.6e}"
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'********3.141593e+00'
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>>> old_price, new_price = 499, 672
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>>> "{:.2%} price increase".format(Fraction(new_price, old_price) - 1)
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'34.67% price increase'
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.. seealso::
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@ -269,6 +269,12 @@ dis
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:data:`~dis.hasarg` collection instead.
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(Contributed by Irit Katriel in :gh:`94216`.)
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fractions
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---------
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* Objects of type :class:`fractions.Fraction` now support float-style
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formatting. (Contributed by Mark Dickinson in :gh:`100161`.)
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math
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----
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206
Lib/fractions.py
206
Lib/fractions.py
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@ -69,6 +69,96 @@ def _hash_algorithm(numerator, denominator):
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""", re.VERBOSE | re.IGNORECASE)
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# Helpers for formatting
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def _round_to_exponent(n, d, exponent, no_neg_zero=False):
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"""Round a rational number to the nearest multiple of a given power of 10.
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Rounds the rational number n/d to the nearest integer multiple of
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10**exponent, rounding to the nearest even integer multiple in the case of
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a tie. Returns a pair (sign: bool, significand: int) representing the
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rounded value (-1)**sign * significand * 10**exponent.
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If no_neg_zero is true, then the returned sign will always be False when
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the significand is zero. Otherwise, the sign reflects the sign of the
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input.
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d must be positive, but n and d need not be relatively prime.
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"""
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if exponent >= 0:
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d *= 10**exponent
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else:
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n *= 10**-exponent
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# The divmod quotient is correct for round-ties-towards-positive-infinity;
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# In the case of a tie, we zero out the least significant bit of q.
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q, r = divmod(n + (d >> 1), d)
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if r == 0 and d & 1 == 0:
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q &= -2
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sign = q < 0 if no_neg_zero else n < 0
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return sign, abs(q)
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def _round_to_figures(n, d, figures):
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"""Round a rational number to a given number of significant figures.
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Rounds the rational number n/d to the given number of significant figures
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using the round-ties-to-even rule, and returns a triple
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(sign: bool, significand: int, exponent: int) representing the rounded
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value (-1)**sign * significand * 10**exponent.
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In the special case where n = 0, returns a significand of zero and
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an exponent of 1 - figures, for compatibility with formatting.
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Otherwise, the returned significand satisfies
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10**(figures - 1) <= significand < 10**figures.
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d must be positive, but n and d need not be relatively prime.
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figures must be positive.
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"""
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# Special case for n == 0.
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if n == 0:
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return False, 0, 1 - figures
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# Find integer m satisfying 10**(m - 1) <= abs(n)/d <= 10**m. (If abs(n)/d
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# is a power of 10, either of the two possible values for m is fine.)
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str_n, str_d = str(abs(n)), str(d)
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m = len(str_n) - len(str_d) + (str_d <= str_n)
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# Round to a multiple of 10**(m - figures). The significand we get
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# satisfies 10**(figures - 1) <= significand <= 10**figures.
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exponent = m - figures
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sign, significand = _round_to_exponent(n, d, exponent)
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# Adjust in the case where significand == 10**figures, to ensure that
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# 10**(figures - 1) <= significand < 10**figures.
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if len(str(significand)) == figures + 1:
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significand //= 10
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exponent += 1
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return sign, significand, exponent
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# Pattern for matching float-style format specifications;
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# supports 'e', 'E', 'f', 'F', 'g', 'G' and '%' presentation types.
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_FLOAT_FORMAT_SPECIFICATION_MATCHER = re.compile(r"""
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(?:
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(?P<fill>.)?
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(?P<align>[<>=^])
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)?
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(?P<sign>[-+ ]?)
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(?P<no_neg_zero>z)?
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(?P<alt>\#)?
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# A '0' that's *not* followed by another digit is parsed as a minimum width
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# rather than a zeropad flag.
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(?P<zeropad>0(?=[0-9]))?
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(?P<minimumwidth>0|[1-9][0-9]*)?
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(?P<thousands_sep>[,_])?
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(?:\.(?P<precision>0|[1-9][0-9]*))?
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(?P<presentation_type>[eEfFgG%])
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""", re.DOTALL | re.VERBOSE).fullmatch
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class Fraction(numbers.Rational):
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"""This class implements rational numbers.
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@ -314,6 +404,122 @@ def __str__(self):
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else:
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return '%s/%s' % (self._numerator, self._denominator)
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def __format__(self, format_spec, /):
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"""Format this fraction according to the given format specification."""
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# Backwards compatiblility with existing formatting.
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if not format_spec:
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return str(self)
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# Validate and parse the format specifier.
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match = _FLOAT_FORMAT_SPECIFICATION_MATCHER(format_spec)
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if match is None:
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raise ValueError(
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f"Invalid format specifier {format_spec!r} "
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f"for object of type {type(self).__name__!r}"
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)
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elif match["align"] is not None and match["zeropad"] is not None:
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# Avoid the temptation to guess.
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raise ValueError(
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f"Invalid format specifier {format_spec!r} "
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f"for object of type {type(self).__name__!r}; "
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"can't use explicit alignment when zero-padding"
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)
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fill = match["fill"] or " "
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align = match["align"] or ">"
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pos_sign = "" if match["sign"] == "-" else match["sign"]
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no_neg_zero = bool(match["no_neg_zero"])
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alternate_form = bool(match["alt"])
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zeropad = bool(match["zeropad"])
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minimumwidth = int(match["minimumwidth"] or "0")
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thousands_sep = match["thousands_sep"]
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precision = int(match["precision"] or "6")
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presentation_type = match["presentation_type"]
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trim_zeros = presentation_type in "gG" and not alternate_form
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trim_point = not alternate_form
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exponent_indicator = "E" if presentation_type in "EFG" else "e"
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# Round to get the digits we need, figure out where to place the point,
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# and decide whether to use scientific notation. 'point_pos' is the
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# relative to the _end_ of the digit string: that is, it's the number
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# of digits that should follow the point.
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if presentation_type in "fF%":
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exponent = -precision
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if presentation_type == "%":
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exponent -= 2
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negative, significand = _round_to_exponent(
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self._numerator, self._denominator, exponent, no_neg_zero)
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scientific = False
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point_pos = precision
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else: # presentation_type in "eEgG"
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figures = (
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max(precision, 1)
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if presentation_type in "gG"
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else precision + 1
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)
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negative, significand, exponent = _round_to_figures(
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self._numerator, self._denominator, figures)
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scientific = (
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presentation_type in "eE"
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or exponent > 0
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or exponent + figures <= -4
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)
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point_pos = figures - 1 if scientific else -exponent
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# Get the suffix - the part following the digits, if any.
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if presentation_type == "%":
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suffix = "%"
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elif scientific:
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suffix = f"{exponent_indicator}{exponent + point_pos:+03d}"
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else:
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suffix = ""
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# String of output digits, padded sufficiently with zeros on the left
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# so that we'll have at least one digit before the decimal point.
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digits = f"{significand:0{point_pos + 1}d}"
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# Before padding, the output has the form f"{sign}{leading}{trailing}",
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# where `leading` includes thousands separators if necessary and
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# `trailing` includes the decimal separator where appropriate.
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sign = "-" if negative else pos_sign
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leading = digits[: len(digits) - point_pos]
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frac_part = digits[len(digits) - point_pos :]
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if trim_zeros:
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frac_part = frac_part.rstrip("0")
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separator = "" if trim_point and not frac_part else "."
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trailing = separator + frac_part + suffix
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# Do zero padding if required.
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if zeropad:
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min_leading = minimumwidth - len(sign) - len(trailing)
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# When adding thousands separators, they'll be added to the
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# zero-padded portion too, so we need to compensate.
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leading = leading.zfill(
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3 * min_leading // 4 + 1 if thousands_sep else min_leading
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)
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# Insert thousands separators if required.
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if thousands_sep:
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first_pos = 1 + (len(leading) - 1) % 3
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leading = leading[:first_pos] + "".join(
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thousands_sep + leading[pos : pos + 3]
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for pos in range(first_pos, len(leading), 3)
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)
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# We now have a sign and a body. Pad with fill character if necessary
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# and return.
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body = leading + trailing
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padding = fill * (minimumwidth - len(sign) - len(body))
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if align == ">":
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return padding + sign + body
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elif align == "<":
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return sign + body + padding
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elif align == "^":
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half = len(padding) // 2
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return padding[:half] + sign + body + padding[half:]
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else: # align == "="
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return sign + padding + body
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def _operator_fallbacks(monomorphic_operator, fallback_operator):
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"""Generates forward and reverse operators given a purely-rational
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operator and a function from the operator module.
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@ -843,6 +843,382 @@ def denominator(self):
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self.assertEqual(type(f.numerator), myint)
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self.assertEqual(type(f.denominator), myint)
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def test_format_no_presentation_type(self):
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# Triples (fraction, specification, expected_result)
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testcases = [
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(F(1, 3), '', '1/3'),
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(F(-1, 3), '', '-1/3'),
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(F(3), '', '3'),
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(F(-3), '', '-3'),
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]
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for fraction, spec, expected in testcases:
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with self.subTest(fraction=fraction, spec=spec):
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self.assertEqual(format(fraction, spec), expected)
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def test_format_e_presentation_type(self):
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# Triples (fraction, specification, expected_result)
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testcases = [
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(F(2, 3), '.6e', '6.666667e-01'),
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(F(3, 2), '.6e', '1.500000e+00'),
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(F(2, 13), '.6e', '1.538462e-01'),
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(F(2, 23), '.6e', '8.695652e-02'),
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(F(2, 33), '.6e', '6.060606e-02'),
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(F(13, 2), '.6e', '6.500000e+00'),
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(F(20, 2), '.6e', '1.000000e+01'),
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(F(23, 2), '.6e', '1.150000e+01'),
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(F(33, 2), '.6e', '1.650000e+01'),
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(F(2, 3), '.6e', '6.666667e-01'),
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(F(3, 2), '.6e', '1.500000e+00'),
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# Zero
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(F(0), '.3e', '0.000e+00'),
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# Powers of 10, to exercise the log10 boundary logic
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(F(1, 1000), '.3e', '1.000e-03'),
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(F(1, 100), '.3e', '1.000e-02'),
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(F(1, 10), '.3e', '1.000e-01'),
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(F(1, 1), '.3e', '1.000e+00'),
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(F(10), '.3e', '1.000e+01'),
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(F(100), '.3e', '1.000e+02'),
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(F(1000), '.3e', '1.000e+03'),
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# Boundary where we round up to the next power of 10
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(F('99.999994999999'), '.6e', '9.999999e+01'),
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(F('99.999995'), '.6e', '1.000000e+02'),
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(F('99.999995000001'), '.6e', '1.000000e+02'),
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# Negatives
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(F(-2, 3), '.6e', '-6.666667e-01'),
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(F(-3, 2), '.6e', '-1.500000e+00'),
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(F(-100), '.6e', '-1.000000e+02'),
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# Large and small
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(F('1e1000'), '.3e', '1.000e+1000'),
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(F('1e-1000'), '.3e', '1.000e-1000'),
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# Using 'E' instead of 'e' should give us a capital 'E'
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(F(2, 3), '.6E', '6.666667E-01'),
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# Tiny precision
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(F(2, 3), '.1e', '6.7e-01'),
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(F('0.995'), '.0e', '1e+00'),
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# Default precision is 6
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(F(22, 7), 'e', '3.142857e+00'),
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# Alternate form forces a decimal point
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(F('0.995'), '#.0e', '1.e+00'),
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# Check that padding takes the exponent into account.
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(F(22, 7), '11.6e', '3.142857e+00'),
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(F(22, 7), '12.6e', '3.142857e+00'),
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(F(22, 7), '13.6e', ' 3.142857e+00'),
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# Thousands separators
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(F('1234567.123456'), ',.5e', '1.23457e+06'),
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(F('123.123456'), '012_.2e', '0_001.23e+02'),
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# z flag is legal, but never makes a difference to the output
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(F(-1, 7**100), 'z.6e', '-3.091690e-85'),
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]
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for fraction, spec, expected in testcases:
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with self.subTest(fraction=fraction, spec=spec):
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self.assertEqual(format(fraction, spec), expected)
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def test_format_f_presentation_type(self):
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# Triples (fraction, specification, expected_result)
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testcases = [
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# Simple .f formatting
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(F(0, 1), '.2f', '0.00'),
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(F(1, 3), '.2f', '0.33'),
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(F(2, 3), '.2f', '0.67'),
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(F(4, 3), '.2f', '1.33'),
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(F(1, 8), '.2f', '0.12'),
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(F(3, 8), '.2f', '0.38'),
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(F(1, 13), '.2f', '0.08'),
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(F(1, 199), '.2f', '0.01'),
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(F(1, 200), '.2f', '0.00'),
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(F(22, 7), '.5f', '3.14286'),
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(F('399024789'), '.2f', '399024789.00'),
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# Large precision (more than float can provide)
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(F(104348, 33215), '.50f',
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'3.14159265392142104470871594159265392142104470871594'),
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# Precision defaults to 6 if not given
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(F(22, 7), 'f', '3.142857'),
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(F(0), 'f', '0.000000'),
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(F(-22, 7), 'f', '-3.142857'),
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# Round-ties-to-even checks
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(F('1.225'), '.2f', '1.22'),
|
||||
(F('1.2250000001'), '.2f', '1.23'),
|
||||
(F('1.2349999999'), '.2f', '1.23'),
|
||||
(F('1.235'), '.2f', '1.24'),
|
||||
(F('1.245'), '.2f', '1.24'),
|
||||
(F('1.2450000001'), '.2f', '1.25'),
|
||||
(F('1.2549999999'), '.2f', '1.25'),
|
||||
(F('1.255'), '.2f', '1.26'),
|
||||
(F('-1.225'), '.2f', '-1.22'),
|
||||
(F('-1.2250000001'), '.2f', '-1.23'),
|
||||
(F('-1.2349999999'), '.2f', '-1.23'),
|
||||
(F('-1.235'), '.2f', '-1.24'),
|
||||
(F('-1.245'), '.2f', '-1.24'),
|
||||
(F('-1.2450000001'), '.2f', '-1.25'),
|
||||
(F('-1.2549999999'), '.2f', '-1.25'),
|
||||
(F('-1.255'), '.2f', '-1.26'),
|
||||
# Negatives and sign handling
|
||||
(F(2, 3), '.2f', '0.67'),
|
||||
(F(2, 3), '-.2f', '0.67'),
|
||||
(F(2, 3), '+.2f', '+0.67'),
|
||||
(F(2, 3), ' .2f', ' 0.67'),
|
||||
(F(-2, 3), '.2f', '-0.67'),
|
||||
(F(-2, 3), '-.2f', '-0.67'),
|
||||
(F(-2, 3), '+.2f', '-0.67'),
|
||||
(F(-2, 3), ' .2f', '-0.67'),
|
||||
# Formatting to zero places
|
||||
(F(1, 2), '.0f', '0'),
|
||||
(F(-1, 2), '.0f', '-0'),
|
||||
(F(22, 7), '.0f', '3'),
|
||||
(F(-22, 7), '.0f', '-3'),
|
||||
# Formatting to zero places, alternate form
|
||||
(F(1, 2), '#.0f', '0.'),
|
||||
(F(-1, 2), '#.0f', '-0.'),
|
||||
(F(22, 7), '#.0f', '3.'),
|
||||
(F(-22, 7), '#.0f', '-3.'),
|
||||
# z flag for suppressing negative zeros
|
||||
(F('-0.001'), 'z.2f', '0.00'),
|
||||
(F('-0.001'), '-z.2f', '0.00'),
|
||||
(F('-0.001'), '+z.2f', '+0.00'),
|
||||
(F('-0.001'), ' z.2f', ' 0.00'),
|
||||
(F('0.001'), 'z.2f', '0.00'),
|
||||
(F('0.001'), '-z.2f', '0.00'),
|
||||
(F('0.001'), '+z.2f', '+0.00'),
|
||||
(F('0.001'), ' z.2f', ' 0.00'),
|
||||
# Specifying a minimum width
|
||||
(F(2, 3), '6.2f', ' 0.67'),
|
||||
(F(12345), '6.2f', '12345.00'),
|
||||
(F(12345), '12f', '12345.000000'),
|
||||
# Fill and alignment
|
||||
(F(2, 3), '>6.2f', ' 0.67'),
|
||||
(F(2, 3), '<6.2f', '0.67 '),
|
||||
(F(2, 3), '^3.2f', '0.67'),
|
||||
(F(2, 3), '^4.2f', '0.67'),
|
||||
(F(2, 3), '^5.2f', '0.67 '),
|
||||
(F(2, 3), '^6.2f', ' 0.67 '),
|
||||
(F(2, 3), '^7.2f', ' 0.67 '),
|
||||
(F(2, 3), '^8.2f', ' 0.67 '),
|
||||
# '=' alignment
|
||||
(F(-2, 3), '=+8.2f', '- 0.67'),
|
||||
(F(2, 3), '=+8.2f', '+ 0.67'),
|
||||
# Fill character
|
||||
(F(-2, 3), 'X>3.2f', '-0.67'),
|
||||
(F(-2, 3), 'X>7.2f', 'XX-0.67'),
|
||||
(F(-2, 3), 'X<7.2f', '-0.67XX'),
|
||||
(F(-2, 3), 'X^7.2f', 'X-0.67X'),
|
||||
(F(-2, 3), 'X=7.2f', '-XX0.67'),
|
||||
(F(-2, 3), ' >7.2f', ' -0.67'),
|
||||
# Corner cases: weird fill characters
|
||||
(F(-2, 3), '\x00>7.2f', '\x00\x00-0.67'),
|
||||
(F(-2, 3), '\n>7.2f', '\n\n-0.67'),
|
||||
(F(-2, 3), '\t>7.2f', '\t\t-0.67'),
|
||||
(F(-2, 3), '>>7.2f', '>>-0.67'),
|
||||
(F(-2, 3), '<>7.2f', '<<-0.67'),
|
||||
(F(-2, 3), '→>7.2f', '→→-0.67'),
|
||||
# Zero-padding
|
||||
(F(-2, 3), '07.2f', '-000.67'),
|
||||
(F(-2, 3), '-07.2f', '-000.67'),
|
||||
(F(2, 3), '+07.2f', '+000.67'),
|
||||
(F(2, 3), ' 07.2f', ' 000.67'),
|
||||
# An isolated zero is a minimum width, not a zero-pad flag.
|
||||
# So unlike zero-padding, it's legal in combination with alignment.
|
||||
(F(2, 3), '0.2f', '0.67'),
|
||||
(F(2, 3), '>0.2f', '0.67'),
|
||||
(F(2, 3), '<0.2f', '0.67'),
|
||||
(F(2, 3), '^0.2f', '0.67'),
|
||||
(F(2, 3), '=0.2f', '0.67'),
|
||||
# Corner case: zero-padding _and_ a zero minimum width.
|
||||
(F(2, 3), '00.2f', '0.67'),
|
||||
# Thousands separator (only affects portion before the point)
|
||||
(F(2, 3), ',.2f', '0.67'),
|
||||
(F(2, 3), ',.7f', '0.6666667'),
|
||||
(F('123456.789'), ',.2f', '123,456.79'),
|
||||
(F('1234567'), ',.2f', '1,234,567.00'),
|
||||
(F('12345678'), ',.2f', '12,345,678.00'),
|
||||
(F('12345678'), ',f', '12,345,678.000000'),
|
||||
# Underscore as thousands separator
|
||||
(F(2, 3), '_.2f', '0.67'),
|
||||
(F(2, 3), '_.7f', '0.6666667'),
|
||||
(F('123456.789'), '_.2f', '123_456.79'),
|
||||
(F('1234567'), '_.2f', '1_234_567.00'),
|
||||
(F('12345678'), '_.2f', '12_345_678.00'),
|
||||
# Thousands and zero-padding
|
||||
(F('1234.5678'), '07,.2f', '1,234.57'),
|
||||
(F('1234.5678'), '08,.2f', '1,234.57'),
|
||||
(F('1234.5678'), '09,.2f', '01,234.57'),
|
||||
(F('1234.5678'), '010,.2f', '001,234.57'),
|
||||
(F('1234.5678'), '011,.2f', '0,001,234.57'),
|
||||
(F('1234.5678'), '012,.2f', '0,001,234.57'),
|
||||
(F('1234.5678'), '013,.2f', '00,001,234.57'),
|
||||
(F('1234.5678'), '014,.2f', '000,001,234.57'),
|
||||
(F('1234.5678'), '015,.2f', '0,000,001,234.57'),
|
||||
(F('1234.5678'), '016,.2f', '0,000,001,234.57'),
|
||||
(F('-1234.5678'), '07,.2f', '-1,234.57'),
|
||||
(F('-1234.5678'), '08,.2f', '-1,234.57'),
|
||||
(F('-1234.5678'), '09,.2f', '-1,234.57'),
|
||||
(F('-1234.5678'), '010,.2f', '-01,234.57'),
|
||||
(F('-1234.5678'), '011,.2f', '-001,234.57'),
|
||||
(F('-1234.5678'), '012,.2f', '-0,001,234.57'),
|
||||
(F('-1234.5678'), '013,.2f', '-0,001,234.57'),
|
||||
(F('-1234.5678'), '014,.2f', '-00,001,234.57'),
|
||||
(F('-1234.5678'), '015,.2f', '-000,001,234.57'),
|
||||
(F('-1234.5678'), '016,.2f', '-0,000,001,234.57'),
|
||||
# Corner case: no decimal point
|
||||
(F('-1234.5678'), '06,.0f', '-1,235'),
|
||||
(F('-1234.5678'), '07,.0f', '-01,235'),
|
||||
(F('-1234.5678'), '08,.0f', '-001,235'),
|
||||
(F('-1234.5678'), '09,.0f', '-0,001,235'),
|
||||
# Corner-case - zero-padding specified through fill and align
|
||||
# instead of the zero-pad character - in this case, treat '0' as a
|
||||
# regular fill character and don't attempt to insert commas into
|
||||
# the filled portion. This differs from the int and float
|
||||
# behaviour.
|
||||
(F('1234.5678'), '0=12,.2f', '00001,234.57'),
|
||||
# Corner case where it's not clear whether the '0' indicates zero
|
||||
# padding or gives the minimum width, but there's still an obvious
|
||||
# answer to give. We want this to work in case the minimum width
|
||||
# is being inserted programmatically: spec = f'{width}.2f'.
|
||||
(F('12.34'), '0.2f', '12.34'),
|
||||
(F('12.34'), 'X>0.2f', '12.34'),
|
||||
# 'F' should work identically to 'f'
|
||||
(F(22, 7), '.5F', '3.14286'),
|
||||
# %-specifier
|
||||
(F(22, 7), '.2%', '314.29%'),
|
||||
(F(1, 7), '.2%', '14.29%'),
|
||||
(F(1, 70), '.2%', '1.43%'),
|
||||
(F(1, 700), '.2%', '0.14%'),
|
||||
(F(1, 7000), '.2%', '0.01%'),
|
||||
(F(1, 70000), '.2%', '0.00%'),
|
||||
(F(1, 7), '.0%', '14%'),
|
||||
(F(1, 7), '#.0%', '14.%'),
|
||||
(F(100, 7), ',.2%', '1,428.57%'),
|
||||
(F(22, 7), '7.2%', '314.29%'),
|
||||
(F(22, 7), '8.2%', ' 314.29%'),
|
||||
(F(22, 7), '08.2%', '0314.29%'),
|
||||
# Test cases from #67790 and discuss.python.org Ideas thread.
|
||||
(F(1, 3), '.2f', '0.33'),
|
||||
(F(1, 8), '.2f', '0.12'),
|
||||
(F(3, 8), '.2f', '0.38'),
|
||||
(F(2545, 1000), '.2f', '2.54'),
|
||||
(F(2549, 1000), '.2f', '2.55'),
|
||||
(F(2635, 1000), '.2f', '2.64'),
|
||||
(F(1, 100), '.1f', '0.0'),
|
||||
(F(49, 1000), '.1f', '0.0'),
|
||||
(F(51, 1000), '.1f', '0.1'),
|
||||
(F(149, 1000), '.1f', '0.1'),
|
||||
(F(151, 1000), '.1f', '0.2'),
|
||||
]
|
||||
for fraction, spec, expected in testcases:
|
||||
with self.subTest(fraction=fraction, spec=spec):
|
||||
self.assertEqual(format(fraction, spec), expected)
|
||||
|
||||
def test_format_g_presentation_type(self):
|
||||
# Triples (fraction, specification, expected_result)
|
||||
testcases = [
|
||||
(F('0.000012345678'), '.6g', '1.23457e-05'),
|
||||
(F('0.00012345678'), '.6g', '0.000123457'),
|
||||
(F('0.0012345678'), '.6g', '0.00123457'),
|
||||
(F('0.012345678'), '.6g', '0.0123457'),
|
||||
(F('0.12345678'), '.6g', '0.123457'),
|
||||
(F('1.2345678'), '.6g', '1.23457'),
|
||||
(F('12.345678'), '.6g', '12.3457'),
|
||||
(F('123.45678'), '.6g', '123.457'),
|
||||
(F('1234.5678'), '.6g', '1234.57'),
|
||||
(F('12345.678'), '.6g', '12345.7'),
|
||||
(F('123456.78'), '.6g', '123457'),
|
||||
(F('1234567.8'), '.6g', '1.23457e+06'),
|
||||
# Rounding up cases
|
||||
(F('9.99999e+2'), '.4g', '1000'),
|
||||
(F('9.99999e-8'), '.4g', '1e-07'),
|
||||
(F('9.99999e+8'), '.4g', '1e+09'),
|
||||
# Check round-ties-to-even behaviour
|
||||
(F('-0.115'), '.2g', '-0.12'),
|
||||
(F('-0.125'), '.2g', '-0.12'),
|
||||
(F('-0.135'), '.2g', '-0.14'),
|
||||
(F('-0.145'), '.2g', '-0.14'),
|
||||
(F('0.115'), '.2g', '0.12'),
|
||||
(F('0.125'), '.2g', '0.12'),
|
||||
(F('0.135'), '.2g', '0.14'),
|
||||
(F('0.145'), '.2g', '0.14'),
|
||||
# Trailing zeros and decimal point suppressed by default ...
|
||||
(F(0), '.6g', '0'),
|
||||
(F('123.400'), '.6g', '123.4'),
|
||||
(F('123.000'), '.6g', '123'),
|
||||
(F('120.000'), '.6g', '120'),
|
||||
(F('12000000'), '.6g', '1.2e+07'),
|
||||
# ... but not when alternate form is in effect
|
||||
(F(0), '#.6g', '0.00000'),
|
||||
(F('123.400'), '#.6g', '123.400'),
|
||||
(F('123.000'), '#.6g', '123.000'),
|
||||
(F('120.000'), '#.6g', '120.000'),
|
||||
(F('12000000'), '#.6g', '1.20000e+07'),
|
||||
# 'G' format (uses 'E' instead of 'e' for the exponent indicator)
|
||||
(F('123.45678'), '.6G', '123.457'),
|
||||
(F('1234567.8'), '.6G', '1.23457E+06'),
|
||||
# Default precision is 6 significant figures
|
||||
(F('3.1415926535'), 'g', '3.14159'),
|
||||
# Precision 0 is treated the same as precision 1.
|
||||
(F('0.000031415'), '.0g', '3e-05'),
|
||||
(F('0.00031415'), '.0g', '0.0003'),
|
||||
(F('0.31415'), '.0g', '0.3'),
|
||||
(F('3.1415'), '.0g', '3'),
|
||||
(F('3.1415'), '#.0g', '3.'),
|
||||
(F('31.415'), '.0g', '3e+01'),
|
||||
(F('31.415'), '#.0g', '3.e+01'),
|
||||
(F('0.000031415'), '.1g', '3e-05'),
|
||||
(F('0.00031415'), '.1g', '0.0003'),
|
||||
(F('0.31415'), '.1g', '0.3'),
|
||||
(F('3.1415'), '.1g', '3'),
|
||||
(F('3.1415'), '#.1g', '3.'),
|
||||
(F('31.415'), '.1g', '3e+01'),
|
||||
# Thousands separator
|
||||
(F(2**64), '_.25g', '18_446_744_073_709_551_616'),
|
||||
# As with 'e' format, z flag is legal, but has no effect
|
||||
(F(-1, 7**100), 'zg', '-3.09169e-85'),
|
||||
]
|
||||
for fraction, spec, expected in testcases:
|
||||
with self.subTest(fraction=fraction, spec=spec):
|
||||
self.assertEqual(format(fraction, spec), expected)
|
||||
|
||||
def test_invalid_formats(self):
|
||||
fraction = F(2, 3)
|
||||
with self.assertRaises(TypeError):
|
||||
format(fraction, None)
|
||||
|
||||
invalid_specs = [
|
||||
'Q6f', # regression test
|
||||
# illegal to use fill or alignment when zero padding
|
||||
'X>010f',
|
||||
'X<010f',
|
||||
'X^010f',
|
||||
'X=010f',
|
||||
'0>010f',
|
||||
'0<010f',
|
||||
'0^010f',
|
||||
'0=010f',
|
||||
'>010f',
|
||||
'<010f',
|
||||
'^010f',
|
||||
'=010e',
|
||||
'=010f',
|
||||
'=010g',
|
||||
'=010%',
|
||||
'>00.2f',
|
||||
'>00f',
|
||||
# Too many zeros - minimum width should not have leading zeros
|
||||
'006f',
|
||||
# Leading zeros in precision
|
||||
'.010f',
|
||||
'.02f',
|
||||
'.000f',
|
||||
# Missing precision
|
||||
'.e',
|
||||
'.f',
|
||||
'.g',
|
||||
'.%',
|
||||
# Z instead of z for negative zero suppression
|
||||
'Z.2f'
|
||||
]
|
||||
for spec in invalid_specs:
|
||||
with self.subTest(spec=spec):
|
||||
with self.assertRaises(ValueError):
|
||||
format(fraction, spec)
|
||||
|
||||
|
||||
if __name__ == '__main__':
|
||||
unittest.main()
|
||||
|
|
|
|||
|
|
@ -0,0 +1,2 @@
|
|||
Add float-style formatting support for :class:`fractions.Fraction`
|
||||
instances.
|
||||
Loading…
Add table
Add a link
Reference in a new issue