diff options
author | Steve Dower <steve.dower@microsoft.com> | 2017-02-04 15:05:40 -0800 |
---|---|---|
committer | Steve Dower <steve.dower@microsoft.com> | 2017-02-04 15:05:40 -0800 |
commit | b2fa705fd3887c326e811c418469c784353027f4 (patch) | |
tree | b3428f73de91453edbfd4df1a5d4a212d182eb44 /Lib/contextlib.py | |
parent | 134e58fd3aaa2e91390041e143f3f0a21a60142b (diff) | |
parent | b53654b6dbfce8318a7d4d1cdaddca7a7fec194b (diff) | |
download | cpython-b2fa705fd3887c326e811c418469c784353027f4.tar.gz |
Issue #29392: Prevent crash when passing invalid arguments into msvcrt module.
Diffstat (limited to 'Lib/contextlib.py')
-rw-r--r-- | Lib/contextlib.py | 42 |
1 files changed, 31 insertions, 11 deletions
diff --git a/Lib/contextlib.py b/Lib/contextlib.py index d44edd6e19..7d94a579c8 100644 --- a/Lib/contextlib.py +++ b/Lib/contextlib.py @@ -1,11 +1,34 @@ """Utilities for with-statement contexts. See PEP 343.""" - +import abc import sys from collections import deque from functools import wraps -__all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack", - "redirect_stdout", "redirect_stderr", "suppress"] +__all__ = ["contextmanager", "closing", "AbstractContextManager", + "ContextDecorator", "ExitStack", "redirect_stdout", + "redirect_stderr", "suppress"] + + +class AbstractContextManager(abc.ABC): + + """An abstract base class for context managers.""" + + def __enter__(self): + """Return `self` upon entering the runtime context.""" + return self + + @abc.abstractmethod + def __exit__(self, exc_type, exc_value, traceback): + """Raise any exception triggered within the runtime context.""" + return None + + @classmethod + def __subclasshook__(cls, C): + if cls is AbstractContextManager: + if (any("__enter__" in B.__dict__ for B in C.__mro__) and + any("__exit__" in B.__dict__ for B in C.__mro__)): + return True + return NotImplemented class ContextDecorator(object): @@ -31,7 +54,7 @@ class ContextDecorator(object): return inner -class _GeneratorContextManager(ContextDecorator): +class _GeneratorContextManager(ContextDecorator, AbstractContextManager): """Helper for @contextmanager decorator.""" def __init__(self, func, args, kwds): @@ -137,7 +160,7 @@ def contextmanager(func): return helper -class closing(object): +class closing(AbstractContextManager): """Context to automatically close something at the end of a block. Code like this: @@ -162,7 +185,7 @@ class closing(object): self.thing.close() -class _RedirectStream: +class _RedirectStream(AbstractContextManager): _stream = None @@ -202,7 +225,7 @@ class redirect_stderr(_RedirectStream): _stream = "stderr" -class suppress: +class suppress(AbstractContextManager): """Context manager to suppress specified exceptions After the exception is suppressed, execution proceeds with the next @@ -233,7 +256,7 @@ class suppress: # Inspired by discussions on http://bugs.python.org/issue13585 -class ExitStack(object): +class ExitStack(AbstractContextManager): """Context manager for dynamic management of a stack of exit callbacks For example: @@ -312,9 +335,6 @@ class ExitStack(object): """Immediately unwind the context stack""" self.__exit__(None, None, None) - def __enter__(self): - return self - def __exit__(self, *exc_details): received_exc = exc_details[0] is not None |