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cpython/Lib/contextlib.py

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Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
"""Utilities for with-statement contexts. See PEP 343."""
import sys
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
__all__ = ["contextmanager", "nested", "closing"]
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
class GeneratorContextManager(object):
"""Helper for @contextmanager decorator."""
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
def __init__(self, gen):
self.gen = gen
def __enter__(self):
try:
return self.gen.next()
except StopIteration:
raise RuntimeError("generator didn't yield")
def __exit__(self, type, value, traceback):
if type is None:
try:
self.gen.next()
except StopIteration:
return
else:
raise RuntimeError("generator didn't stop")
else:
try:
self.gen.throw(type, value, traceback)
Fix a problem with @contextmanager not detecting a broken generator that yields after a throw(). Make @contextmanager not reraise exceptions, but return a false value in that case instead. Add test cases for both behaviors.
2006-03-25 00:28:24 +00:00
raise RuntimeError("generator didn't stop after throw()")
Minor clarity edit to contextlib per Guido's request.
2006-04-10 17:56:29 +00:00
except StopIteration, exc:
Fix typos; enhance comments on patch for SF #1462485. --This line, and those below, will be ignored-- M contextlib.py
2006-04-03 21:20:07 +00:00
# Suppress the exception *unless* it's the same exception that
# was passed to throw(). This prevents a StopIteration
# raised inside the "with" statement from being suppressed
Minor clarity edit to contextlib per Guido's request.
2006-04-10 17:56:29 +00:00
return exc is not value
Fix a problem with @contextmanager not detecting a broken generator that yields after a throw(). Make @contextmanager not reraise exceptions, but return a false value in that case instead. Add test cases for both behaviors.
2006-03-25 00:28:24 +00:00
except:
More extensive comment on __exit__ handling, per Guido's request.
2006-03-25 04:32:12 +00:00
# only re-raise if it's *not* the exception that was
# passed to throw(), because __exit__() must not raise
# an exception unless __exit__() itself failed. But throw()
# has to raise the exception to signal propagation, so this
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
#
Fix a problem with @contextmanager not detecting a broken generator that yields after a throw(). Make @contextmanager not reraise exceptions, but return a false value in that case instead. Add test cases for both behaviors.
2006-03-25 00:28:24 +00:00
if sys.exc_info()[1] is not value:
raise
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
def contextmanager(func):
"""@contextmanager decorator.
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
Typical usage:
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
@contextmanager
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
def some_generator(<arguments>):
<setup>
try:
yield <value>
finally:
<cleanup>
This makes this:
with some_generator(<arguments>) as <variable>:
<body>
equivalent to this:
<setup>
try:
<variable> = <value>
<body>
finally:
<cleanup>
"""
def helper(*args, **kwds):
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
return GeneratorContextManager(func(*args, **kwds))
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
try:
helper.__name__ = func.__name__
helper.__doc__ = func.__doc__
Fix contextlib not copying function attributes
2006-03-28 00:07:24 +00:00
helper.__dict__ = func.__dict__
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
except:
pass
return helper
Finish bringing SVN into line with latest version of PEP 343 by getting rid of all remaining references to context objects that I could find. Without a __context__() method context objects no longer exist. Also get test_with working again, and adopt a suggestion from Neal for decimal.Context.get_manager()
2006-05-03 13:02:47 +00:00
@contextmanager
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
def nested(*managers):
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
"""Support multiple context managers in a single with-statement.
Code like this:
with nested(A, B, C) as (X, Y, Z):
<body>
is equivalent to this:
with A as X:
with B as Y:
with C as Z:
<body>
"""
exits = []
vars = []
Um, I thought I'd already checked this in. Anyway, this is the changes to the with-statement so that __exit__ must return a true value in order for a pending exception to be ignored. The PEP (343) is already updated.
2006-03-10 02:28:35 +00:00
exc = (None, None, None)
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
try:
Use try-except-finally in contextlib.
2007-08-23 18:11:33 +00:00
for mgr in managers:
exit = mgr.__exit__
enter = mgr.__enter__
vars.append(enter())
exits.append(exit)
yield vars
except:
exc = sys.exc_info()
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
finally:
while exits:
exit = exits.pop()
try:
Um, I thought I'd already checked this in. Anyway, this is the changes to the with-statement so that __exit__ must return a true value in order for a pending exception to be ignored. The PEP (343) is already updated.
2006-03-10 02:28:35 +00:00
if exit(*exc):
exc = (None, None, None)
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
except:
exc = sys.exc_info()
if exc != (None, None, None):
Fix contextlib.nested to cope with exit methods raising and handling exceptions
2006-04-24 04:37:15 +00:00
# Don't rely on sys.exc_info() still containing
# the right information. Another exception may
# have been raised and caught by an exit method
raise exc[0], exc[1], exc[2]
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
Move the PEP 343 documentation and implementation closer to the terminology in the alpha 1 documentation. - "context manager" reverts to its alpha 1 definition - the term "context specifier" goes away entirely - contextlib.GeneratorContextManager is renamed GeneratorContext There are still a number of changes relative to alpha 1: - the expression in the with statement is explicitly called the "context expression" in the language reference - the terms 'with statement context', 'context object' or 'with statement context' are used in several places instead of a bare 'context'. The aim of this is to avoid ambiguity in relation to the runtime context set up when the block is executed, and the context objects that already exist in various application domains (such as decimal.Context) - contextlib.contextmanager is renamed to contextfactory This best reflects the nature of the function resulting from the use of that decorator - decimal.ContextManager is renamed to WithStatementContext Simple dropping the 'Manager' part wasn't possible due to the fact that decimal.Context already exists and means something different. WithStatementContext is ugly but workable. A technically unrelated change snuck into this commit: contextlib.closing now avoids the overhead of creating a generator, since it's trivial to implement that particular context manager directly.
2006-04-25 10:56:51 +00:00
class closing(object):
"""Context to automatically close something at the end of a block.
Updates to the with-statement: - New semantics for __exit__() -- it must re-raise the exception if type is not None; the with-statement itself doesn't do this. (See the updated PEP for motivation.) - Added context managers to: - file - thread.LockType - threading.{Lock,RLock,Condition,Semaphore,BoundedSemaphore} - decimal.Context - Added contextlib.py, which defines @contextmanager, nested(), closing(). - Unit tests all around; bot no docs yet.
2006-02-28 21:57:43 +00:00
Code like this:
with closing(<module>.open(<arguments>)) as f:
<block>
is equivalent to this:
f = <module>.open(<arguments>)
try:
<block>
finally:
f.close()
"""
Move the PEP 343 documentation and implementation closer to the terminology in the alpha 1 documentation. - "context manager" reverts to its alpha 1 definition - the term "context specifier" goes away entirely - contextlib.GeneratorContextManager is renamed GeneratorContext There are still a number of changes relative to alpha 1: - the expression in the with statement is explicitly called the "context expression" in the language reference - the terms 'with statement context', 'context object' or 'with statement context' are used in several places instead of a bare 'context'. The aim of this is to avoid ambiguity in relation to the runtime context set up when the block is executed, and the context objects that already exist in various application domains (such as decimal.Context) - contextlib.contextmanager is renamed to contextfactory This best reflects the nature of the function resulting from the use of that decorator - decimal.ContextManager is renamed to WithStatementContext Simple dropping the 'Manager' part wasn't possible due to the fact that decimal.Context already exists and means something different. WithStatementContext is ugly but workable. A technically unrelated change snuck into this commit: contextlib.closing now avoids the overhead of creating a generator, since it's trivial to implement that particular context manager directly.
2006-04-25 10:56:51 +00:00
def __init__(self, thing):
self.thing = thing
def __enter__(self):
return self.thing
def __exit__(self, *exc_info):
self.thing.close()
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