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Issue #12: sync contextlib from Python 3.10

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Nick Coghlan 2021-06-26 16:36:23 +10:00
parent 94f3881963
commit 17b0a93e5b
1 changed files with 411 additions and 135 deletions
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546
contextlib2.py
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@ -3,15 +3,15 @@
import abc
import sys
import warnings
import _collections_abc
from collections import deque
from functools import wraps
from types import MethodType, GenericAlias
from _collections_abc import _check_methods
__all__ = ["contextmanager", "closing", "nullcontext",
"AbstractContextManager",
"ContextDecorator", "ExitStack",
"redirect_stdout", "redirect_stderr", "suppress"]
__all__ = ["asynccontextmanager", "contextmanager", "closing", "nullcontext",
"AbstractContextManager", "AbstractAsyncContextManager",
"AsyncExitStack", "ContextDecorator", "ExitStack",
"redirect_stdout", "redirect_stderr", "suppress", "aclosing"]
# Backwards compatibility
__all__ += ["ContextStack"]
@ -19,6 +19,8 @@ __all__ += ["ContextStack"]
class AbstractContextManager(abc.ABC):
"""An abstract base class for context managers."""
__class_getitem__ = classmethod(GenericAlias)
def __enter__(self):
"""Return `self` upon entering the runtime context."""
return self
@ -30,31 +32,36 @@ class AbstractContextManager(abc.ABC):
@classmethod
def __subclasshook__(cls, C):
"""Check whether subclass is considered a subclass of this ABC."""
if cls is AbstractContextManager:
return _check_methods(C, "__enter__", "__exit__")
return _collections_abc._check_methods(C, "__enter__", "__exit__")
return NotImplemented
class AbstractAsyncContextManager(abc.ABC):
"""An abstract base class for asynchronous context managers."""
__class_getitem__ = classmethod(GenericAlias)
async def __aenter__(self):
"""Return `self` upon entering the runtime context."""
return self
@abc.abstractmethod
async def __aexit__(self, exc_type, exc_value, traceback):
"""Raise any exception triggered within the runtime context."""
return None
@classmethod
def __subclasshook__(cls, C):
if cls is AbstractAsyncContextManager:
return _collections_abc._check_methods(C, "__aenter__",
"__aexit__")
return NotImplemented
class ContextDecorator(object):
"""A base class or mixin that enables context managers to work as decorators."""
def refresh_cm(self):
"""Returns the context manager used to actually wrap the call to the
decorated function.
The default implementation just returns *self*.
Overriding this method allows otherwise one-shot context managers
like _GeneratorContextManager to support use as decorators via
implicit recreation.
DEPRECATED: refresh_cm was never added to the standard library's
ContextDecorator API
"""
warnings.warn("refresh_cm was never added to the standard library",
DeprecationWarning)
return self._recreate_cm()
"A base class or mixin that enables context managers to work as decorators."
def _recreate_cm(self):
"""Return a recreated instance of self.
@ -76,8 +83,24 @@ class ContextDecorator(object):
return inner
class _GeneratorContextManager(ContextDecorator):
"""Helper for @contextmanager decorator."""
class AsyncContextDecorator(object):
"A base class or mixin that enables async context managers to work as decorators."
def _recreate_cm(self):
"""Return a recreated instance of self.
"""
return self
def __call__(self, func):
@wraps(func)
async def inner(*args, **kwds):
async with self._recreate_cm():
return await func(*args, **kwds)
return inner
class _GeneratorContextManagerBase:
"""Shared functionality for @contextmanager and @asynccontextmanager."""
def __init__(self, func, args, kwds):
self.gen = func(*args, **kwds)
@ -93,6 +116,12 @@ class _GeneratorContextManager(ContextDecorator):
# for the class instead.
# See http://bugs.python.org/issue19404 for more details.
class _GeneratorContextManager(_GeneratorContextManagerBase,
AbstractContextManager,
ContextDecorator):
"""Helper for @contextmanager decorator."""
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
# CM must be recreated each time a decorated function is
@ -100,17 +129,20 @@ class _GeneratorContextManager(ContextDecorator):
return self.__class__(self.func, self.args, self.kwds)
def __enter__(self):
# do not keep args and kwds alive unnecessarily
# they are only needed for recreation, which is not possible anymore
del self.args, self.kwds, self.func
try:
return next(self.gen)
except StopIteration:
raise RuntimeError("generator didn't yield")
raise RuntimeError("generator didn't yield") from None
def __exit__(self, type, value, traceback):
if type is None:
try:
next(self.gen)
except StopIteration:
return
return False
else:
raise RuntimeError("generator didn't stop")
else:
@ -120,20 +152,19 @@ class _GeneratorContextManager(ContextDecorator):
value = type()
try:
self.gen.throw(type, value, traceback)
raise RuntimeError("generator didn't stop after throw()")
except StopIteration as exc:
# Suppress StopIteration *unless* it's the same exception that
# was passed to throw(). This prevents a StopIteration
# raised inside the "with" statement from being suppressed.
return exc is not value
except RuntimeError as exc:
# Don't re-raise the passed in exception
# Don't re-raise the passed in exception. (issue27122)
if exc is value:
return False
# Likewise, avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# (see PEP 479).
if exc.__cause__ is value:
if type is StopIteration and exc.__cause__ is value:
return False
raise
except:
@ -144,7 +175,66 @@ class _GeneratorContextManager(ContextDecorator):
# fixes the impedance mismatch between the throw() protocol
# and the __exit__() protocol.
#
if sys.exc_info()[1] is not value:
# This cannot use 'except BaseException as exc' (as in the
# async implementation) to maintain compatibility with
# Python 2, where old-style class exceptions are not caught
# by 'except BaseException'.
if sys.exc_info()[1] is value:
return False
raise
raise RuntimeError("generator didn't stop after throw()")
class _AsyncGeneratorContextManager(_GeneratorContextManagerBase,
AbstractAsyncContextManager,
AsyncContextDecorator):
"""Helper for @asynccontextmanager."""
def _recreate_cm(self):
# _AGCM instances are one-shot context managers, so the
# ACM must be recreated each time a decorated function is
# called
return self.__class__(self.func, self.args, self.kwds)
async def __aenter__(self):
try:
return await self.gen.__anext__()
except StopAsyncIteration:
raise RuntimeError("generator didn't yield") from None
async def __aexit__(self, typ, value, traceback):
if typ is None:
try:
await self.gen.__anext__()
except StopAsyncIteration:
return
else:
raise RuntimeError("generator didn't stop")
else:
if value is None:
value = typ()
# See _GeneratorContextManager.__exit__ for comments on subtleties
# in this implementation
try:
await self.gen.athrow(typ, value, traceback)
raise RuntimeError("generator didn't stop after athrow()")
except StopAsyncIteration as exc:
return exc is not value
except RuntimeError as exc:
if exc is value:
return False
# Avoid suppressing if a StopIteration exception
# was passed to throw() and later wrapped into a RuntimeError
# (see PEP 479 for sync generators; async generators also
# have this behavior). But do this only if the exception wrapped
# by the RuntimeError is actually Stop(Async)Iteration (see
# issue29692).
if isinstance(value, (StopIteration, StopAsyncIteration)):
if exc.__cause__ is value:
return False
raise
except BaseException as exc:
if exc is not value:
raise
@ -174,7 +264,6 @@ def contextmanager(func):
<body>
finally:
<cleanup>
"""
@wraps(func)
def helper(*args, **kwds):
@ -182,7 +271,40 @@ def contextmanager(func):
return helper
class closing(object):
def asynccontextmanager(func):
"""@asynccontextmanager decorator.
Typical usage:
@asynccontextmanager
async def some_async_generator(<arguments>):
<setup>
try:
yield <value>
finally:
<cleanup>
This makes this:
async with some_async_generator(<arguments>) as <variable>:
<body>
equivalent to this:
<setup>
try:
<variable> = <value>
<body>
finally:
<cleanup>
"""
@wraps(func)
def helper(*args, **kwds):
return _AsyncGeneratorContextManager(func, args, kwds)
return helper
class closing(AbstractContextManager):
"""Context to automatically close something at the end of a block.
Code like this:
@ -201,15 +323,39 @@ class closing(object):
"""
def __init__(self, thing):
self.thing = thing
def __enter__(self):
return self.thing
def __exit__(self, *exc_info):
self.thing.close()
class _RedirectStream(object):
class aclosing(AbstractAsyncContextManager):
"""Async context manager for safely finalizing an asynchronously cleaned-up
resource such as an async generator, calling its ``aclose()`` method.
Code like this:
async with aclosing(<module>.fetch(<arguments>)) as agen:
<block>
is equivalent to this:
agen = <module>.fetch(<arguments>)
try:
<block>
finally:
await agen.aclose()
"""
def __init__(self, thing):
self.thing = thing
async def __aenter__(self):
return self.thing
async def __aexit__(self, *exc_info):
await self.thing.aclose()
class _RedirectStream(AbstractContextManager):
_stream = None
@ -249,7 +395,7 @@ class redirect_stderr(_RedirectStream):
_stream = "stderr"
class suppress(object):
class suppress(AbstractContextManager):
"""Context manager to suppress specified exceptions
After the exception is suppressed, execution proceeds with the next
@ -279,113 +425,96 @@ class suppress(object):
return exctype is not None and issubclass(exctype, self._exceptions)
# Context manipulation helpers
def _make_context_fixer(frame_exc):
def _fix_exception_context(new_exc, old_exc):
# Context may not be correct, so find the end of the chain
while 1:
exc_context = new_exc.__context__
if exc_context is old_exc:
# Context is already set correctly (see issue 20317)
return
if exc_context is None or exc_context is frame_exc:
break
new_exc = exc_context
# Change the end of the chain to point to the exception
# we expect it to reference
new_exc.__context__ = old_exc
return _fix_exception_context
class _BaseExitStack:
"""A base class for ExitStack and AsyncExitStack."""
def _reraise_with_existing_context(exc_details):
try:
# bare "raise exc_details[1]" replaces our carefully
# set-up context
fixed_ctx = exc_details[1].__context__
raise exc_details[1]
except BaseException:
exc_details[1].__context__ = fixed_ctx
raise
@staticmethod
def _create_exit_wrapper(cm, cm_exit):
return MethodType(cm_exit, cm)
@staticmethod
def _create_cb_wrapper(callback, /, *args, **kwds):
def _exit_wrapper(exc_type, exc, tb):
callback(*args, **kwds)
return _exit_wrapper
# Inspired by discussions on http://bugs.python.org/issue13585
class ExitStack(object):
"""Context manager for dynamic management of a stack of exit callbacks
For example:
with ExitStack() as stack:
files = [stack.enter_context(open(fname)) for fname in filenames]
# All opened files will automatically be closed at the end of
# the with statement, even if attempts to open files later
# in the list raise an exception
"""
def __init__(self):
self._exit_callbacks = deque()
def pop_all(self):
"""Preserve the context stack by transferring it to a new instance"""
"""Preserve the context stack by transferring it to a new instance."""
new_stack = type(self)()
new_stack._exit_callbacks = self._exit_callbacks
self._exit_callbacks = deque()
return new_stack
def _push_cm_exit(self, cm, cm_exit):
"""Helper to correctly register callbacks to __exit__ methods"""
def _exit_wrapper(*exc_details):
return cm_exit(cm, *exc_details)
_exit_wrapper.__self__ = cm
self.push(_exit_wrapper)
def push(self, exit):
"""Registers a callback with the standard __exit__ method signature
Can suppress exceptions the same way __exit__ methods can.
"""Registers a callback with the standard __exit__ method signature.
Can suppress exceptions the same way __exit__ method can.
Also accepts any object with an __exit__ method (registering a call
to the method instead of the object itself)
to the method instead of the object itself).
"""
# We use an unbound method rather than a bound method to follow
# the standard lookup behaviour for special methods
# the standard lookup behaviour for special methods.
_cb_type = type(exit)
try:
exit_method = _cb_type.__exit__
except AttributeError:
# Not a context manager, so assume its a callable
self._exit_callbacks.append(exit)
# Not a context manager, so assume it's a callable.
self._push_exit_callback(exit)
else:
self._push_cm_exit(exit, exit_method)
return exit # Allow use as a decorator
def callback(self, callback, *args, **kwds):
"""Registers an arbitrary callback and arguments.
Cannot suppress exceptions.
"""
def _exit_wrapper(exc_type, exc, tb):
callback(*args, **kwds)
# We changed the signature, so using @wraps is not appropriate, but
# setting __wrapped__ may still help with introspection
_exit_wrapper.__wrapped__ = callback
self.push(_exit_wrapper)
return callback # Allow use as a decorator
return exit # Allow use as a decorator.
def enter_context(self, cm):
"""Enters the supplied context manager
"""Enters the supplied context manager.
If successful, also pushes its __exit__ method as a callback and
returns the result of the __enter__ method.
"""
# We look up the special methods on the type to match the with statement
# We look up the special methods on the type to match the with
# statement.
_cm_type = type(cm)
_exit = _cm_type.__exit__
result = _cm_type.__enter__(cm)
self._push_cm_exit(cm, _exit)
return result
def close(self):
"""Immediately unwind the context stack"""
self.__exit__(None, None, None)
def callback(self, callback, /, *args, **kwds):
"""Registers an arbitrary callback and arguments.
Cannot suppress exceptions.
"""
_exit_wrapper = self._create_cb_wrapper(callback, *args, **kwds)
# We changed the signature, so using @wraps is not appropriate, but
# setting __wrapped__ may still help with introspection.
_exit_wrapper.__wrapped__ = callback
self._push_exit_callback(_exit_wrapper)
return callback # Allow use as a decorator
def _push_cm_exit(self, cm, cm_exit):
"""Helper to correctly register callbacks to __exit__ methods."""
_exit_wrapper = self._create_exit_wrapper(cm, cm_exit)
self._push_exit_callback(_exit_wrapper, True)
def _push_exit_callback(self, callback, is_sync=True):
self._exit_callbacks.append((is_sync, callback))
# Inspired by discussions on http://bugs.python.org/issue13585
class ExitStack(_BaseExitStack, AbstractContextManager):
"""Context manager for dynamic management of a stack of exit callbacks.
For example:
with ExitStack() as stack:
files = [stack.enter_context(open(fname)) for fname in filenames]
# All opened files will automatically be closed at the end of
# the with statement, even if attempts to open files later
# in the list raise an exception.
"""
def __enter__(self):
return self
@ -396,14 +525,27 @@ class ExitStack(object):
# We manipulate the exception state so it behaves as though
# we were actually nesting multiple with statements
frame_exc = sys.exc_info()[1]
_fix_exception_context = _make_context_fixer(frame_exc)
def _fix_exception_context(new_exc, old_exc):
# Context may not be correct, so find the end of the chain
while 1:
exc_context = new_exc.__context__
if exc_context is old_exc:
# Context is already set correctly (see issue 20317)
return
if exc_context is None or exc_context is frame_exc:
break
new_exc = exc_context
# Change the end of the chain to point to the exception
# we expect it to reference
new_exc.__context__ = old_exc
# Callbacks are invoked in LIFO order to match the behaviour of
# nested context managers
suppressed_exc = False
pending_raise = False
while self._exit_callbacks:
cb = self._exit_callbacks.pop()
is_sync, cb = self._exit_callbacks.pop()
assert is_sync
try:
if cb(*exc_details):
suppressed_exc = True
@ -416,33 +558,161 @@ class ExitStack(object):
pending_raise = True
exc_details = new_exc_details
if pending_raise:
_reraise_with_existing_context(exc_details)
try:
# bare "raise exc_details[1]" replaces our carefully
# set-up context
fixed_ctx = exc_details[1].__context__
raise exc_details[1]
except BaseException:
exc_details[1].__context__ = fixed_ctx
raise
return received_exc and suppressed_exc
def close(self):
"""Immediately unwind the context stack."""
self.__exit__(None, None, None)
# Inspired by discussions on https://bugs.python.org/issue29302
class AsyncExitStack(_BaseExitStack, AbstractAsyncContextManager):
"""Async context manager for dynamic management of a stack of exit
callbacks.
For example:
async with AsyncExitStack() as stack:
connections = [await stack.enter_async_context(get_connection())
for i in range(5)]
# All opened connections will automatically be released at the
# end of the async with statement, even if attempts to open a
# connection later in the list raise an exception.
"""
@staticmethod
def _create_async_exit_wrapper(cm, cm_exit):
return MethodType(cm_exit, cm)
@staticmethod
def _create_async_cb_wrapper(callback, /, *args, **kwds):
async def _exit_wrapper(exc_type, exc, tb):
await callback(*args, **kwds)
return _exit_wrapper
async def enter_async_context(self, cm):
"""Enters the supplied async context manager.
If successful, also pushes its __aexit__ method as a callback and
returns the result of the __aenter__ method.
"""
_cm_type = type(cm)
_exit = _cm_type.__aexit__
result = await _cm_type.__aenter__(cm)
self._push_async_cm_exit(cm, _exit)
return result
def push_async_exit(self, exit):
"""Registers a coroutine function with the standard __aexit__ method
signature.
Can suppress exceptions the same way __aexit__ method can.
Also accepts any object with an __aexit__ method (registering a call
to the method instead of the object itself).
"""
_cb_type = type(exit)
try:
exit_method = _cb_type.__aexit__
except AttributeError:
# Not an async context manager, so assume it's a coroutine function
self._push_exit_callback(exit, False)
else:
self._push_async_cm_exit(exit, exit_method)
return exit # Allow use as a decorator
def push_async_callback(self, callback, /, *args, **kwds):
"""Registers an arbitrary coroutine function and arguments.
Cannot suppress exceptions.
"""
_exit_wrapper = self._create_async_cb_wrapper(callback, *args, **kwds)
# We changed the signature, so using @wraps is not appropriate, but
# setting __wrapped__ may still help with introspection.
_exit_wrapper.__wrapped__ = callback
self._push_exit_callback(_exit_wrapper, False)
return callback # Allow use as a decorator
async def aclose(self):
"""Immediately unwind the context stack."""
await self.__aexit__(None, None, None)
def _push_async_cm_exit(self, cm, cm_exit):
"""Helper to correctly register coroutine function to __aexit__
method."""
_exit_wrapper = self._create_async_exit_wrapper(cm, cm_exit)
self._push_exit_callback(_exit_wrapper, False)
async def __aenter__(self):
return self
async def __aexit__(self, *exc_details):
received_exc = exc_details[0] is not None
# We manipulate the exception state so it behaves as though
# we were actually nesting multiple with statements
frame_exc = sys.exc_info()[1]
def _fix_exception_context(new_exc, old_exc):
# Context may not be correct, so find the end of the chain
while 1:
exc_context = new_exc.__context__
if exc_context is old_exc:
# Context is already set correctly (see issue 20317)
return
if exc_context is None or exc_context is frame_exc:
break
new_exc = exc_context
# Change the end of the chain to point to the exception
# we expect it to reference
new_exc.__context__ = old_exc
# Callbacks are invoked in LIFO order to match the behaviour of
# nested context managers
suppressed_exc = False
pending_raise = False
while self._exit_callbacks:
is_sync, cb = self._exit_callbacks.pop()
try:
if is_sync:
cb_suppress = cb(*exc_details)
else:
cb_suppress = await cb(*exc_details)
if cb_suppress:
suppressed_exc = True
pending_raise = False
exc_details = (None, None, None)
except:
new_exc_details = sys.exc_info()
# simulate the stack of exceptions by setting the context
_fix_exception_context(new_exc_details[1], exc_details[1])
pending_raise = True
exc_details = new_exc_details
if pending_raise:
try:
# bare "raise exc_details[1]" replaces our carefully
# set-up context
fixed_ctx = exc_details[1].__context__
raise exc_details[1]
except BaseException:
exc_details[1].__context__ = fixed_ctx
raise
return received_exc and suppressed_exc
# Preserve backwards compatibility
class ContextStack(ExitStack):
"""Backwards compatibility alias for ExitStack"""
def __init__(self):
warnings.warn("ContextStack has been renamed to ExitStack",
DeprecationWarning)
super(ContextStack, self).__init__()
def register_exit(self, callback):
return self.push(callback)
def register(self, callback, *args, **kwds):
return self.callback(callback, *args, **kwds)
def preserve(self):
return self.pop_all()
class nullcontext(AbstractContextManager):
class nullcontext(AbstractContextManager, AbstractAsyncContextManager):
"""Context manager that does no additional processing.
Used as a stand-in for a normal context manager, when a particular
block of code is only sometimes used with a normal context manager:
cm = optional_cm if condition else nullcontext()
with cm:
# Perform operation, using optional_cm if condition is True
@ -456,3 +726,9 @@ class nullcontext(AbstractContextManager):
def __exit__(self, *excinfo):
pass
async def __aenter__(self):
return self.enter_result
async def __aexit__(self, *excinfo):
pass