Utilities for
with-statement contexts
__all__ = ["contextmanager", "closing", "AbstractContextManager",
"ContextDecorator", "ExitStack", "redirect_stdout",
"redirect_stderr", "suppress"]
AbstractContextManager(abc.ABC)
上下文管理抽象类，子类必须实现__enter__(self)、__exit__(self)
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
ContextDecorator(object)
上下文管理基类或mixin类，该类可以像装饰器一样工作，提供你需要实现的任何辅助功能
class ContextDecorator(object):
"A base class or mixin that enables context managers to work as decorators."
def _recreate_cm(self):
"""Return a recreated instance of self.
Allows an otherwise one-shot context manager like
_GeneratorContextManager to support use as
a decorator via implicit recreation.
This is a private interface just for _GeneratorContextManager.
See issue #11647 for details.
"""
return self
def __call__(self, func):
@wraps(func)
def inner(*args, **kwds):
with self._recreate_cm():
return func(*args, **kwds)
return inner
_GeneratorContextManager(ContextDecorator, AbstractContextManager)
contextmanager装饰器的包装函数提供以下方法：
_recreate_cm(重新生成新对像)，self.__class__(*args, **kwds)
__enter__上下文管理进入函数
__exit__上下文管理退出函数
可以根据ContextDecorator实现任何想实现的辅助功能
class _GeneratorContextManager(ContextDecorator, AbstractContextManager):
"""Helper for @contextmanager decorator."""
def __init__(self, func, args, kwds):
self.gen = func(*args, **kwds)
logger.info("get generator by with:{}".format(self.gen))
self.func, self.args, self.kwds = func, args, kwds
# Issue 19330: ensure context manager instances have good docstrings
doc = getattr(func, "__doc__", None) #得到函数文档，第三个参数为默认参数
logger.info("doc:{}".format(doc))
if doc is None:
doc = type(self).__doc__
self.__doc__ = doc
# Unfortunately, this still doesn‘t provide good help output when
# inspecting the created context manager instances, since pydoc
# currently bypasses the instance docstring and shows the docstring
# for the class instead.
# See http://bugs.python.org/issue19404 for more details.
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
# CM must be recreated each time a decorated function is
# called
return self.__class__(self.func, self.args, self.kwds)
def __enter__(self):
logger.info("__enter__:you can add you method")
@ContextDecorator()
def testfun(*args, **kwds):
logger.info("@ContextDecorator():testfun test success")
testfun("hello")
try:
return next(self.gen)
except StopIteration:
raise RuntimeError("generator didn‘t yield") from None
def __exit__(self, type, value, traceback):
logger.info("__exit__")
logger.info("type:{}".format(type))
if type is None:
try:
next(self.gen)
except StopIteration:
return
else:
raise RuntimeError("generator didn‘t stop")
else:
if value is None:
# Need to force instantiation so we can reliably
# tell if we get the same exception back
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. (issue27112)
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:
return False
raise
except:
# 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.
#
if sys.exc_info()[1] is not value:
raise
装饰器contextmanager
def contextmanager(func):
"""@contextmanager decorator.
Typical usage:
@contextmanager
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>
"""
@wraps(func)
def helper(*args, **kwds):
return _GeneratorContextManager(func, args, kwds)
return helper
用例：
#coding = utf-8
import abc
from functools import wraps
import logging
logging.basicConfig(level=logging.INFO, filename="logging.txt", filemode="w+", format=‘%(asctime)s - %(name)s - %(levelname)s - %(message)s‘)
logger = logging.getLogger(__name__)
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):
"A base class or mixin that enables context managers to work as decorators."
def _recreate_cm(self):
"""Return a recreated instance of self.
Allows an otherwise one-shot context manager like
_GeneratorContextManager to support use as
a decorator via implicit recreation.
This is a private interface just for _GeneratorContextManager.
See issue #11647 for details.
"""
return self
def __call__(self, func):
#logger.info("ContextDecorator func:{}".format(func))
@wraps(func)
def inner(*args, **kwds):
#with self._recreate_cm():
logger.info("you can do something in decorator")
return func(*args, **kwds)
return inner
class _GeneratorContextManager(ContextDecorator, AbstractContextManager):
"""Helper for @contextmanager decorator."""
def __init__(self, func, args, kwds):
self.gen = func(*args, **kwds)
logger.info("get generator by with:{}".format(self.gen))
self.func, self.args, self.kwds = func, args, kwds
# Issue 19330: ensure context manager instances have good docstrings
doc = getattr(func, "__doc__", None) #得到函数文档，第三个参数为默认参数
logger.info("doc:{}".format(doc))
if doc is None:
doc = type(self).__doc__
self.__doc__ = doc
# Unfortunately, this still doesn‘t provide good help output when
# inspecting the created context manager instances, since pydoc
# currently bypasses the instance docstring and shows the docstring
# for the class instead.
# See http://bugs.python.org/issue19404 for more details.
def _recreate_cm(self):
# _GCM instances are one-shot context managers, so the
# CM must be recreated each time a decorated function is
# called
return self.__class__(self.func, self.args, self.kwds)
def __enter__(self):
logger.info("__enter__:you can add you method")
@ContextDecorator()
def testfun(*args, **kwds):
logger.info("@ContextDecorator():testfun test success")
testfun("hello")
try:
return next(self.gen)
except StopIteration:
raise RuntimeError("generator didn‘t yield") from None
def __exit__(self, type, value, traceback):
logger.info("__exit__")
logger.info("type:{}".format(type))
if type is None:
try:
next(self.gen)
except StopIteration:
return
else:
raise RuntimeError("generator didn‘t stop")
else:
if value is None:
# Need to force instantiation so we can reliably
# tell if we get the same exception back
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. (issue27112)
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:
return False
raise
except:
# 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.
#
if sys.exc_info()[1] is not value:
raise
def contextmanager(func):
"""@contextmanager decorator.
Typical usage:
@contextmanager
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>
"""
@wraps(func)
def helper(*args, **kwds):
return _GeneratorContextManager(func, args, kwds)
return helper
@contextmanager
def file_open(path):
‘‘‘ file open test‘‘‘
try:
f_obj = open(path,"w")
yield f_obj
except OSError:
print("We had an error!")
finally:
print("Closing file")
f_obj.close()
if __name__ == "__main__":
with file_open("contextlibtest.txt") as fobj:
fobj.write("Testing context managers")
logger.info("write file success")
关键输出：
2018-03-22 15:36:43,249 - __main__ - INFO - get generator by with:<generator object file_open at 0x01DE4870> 2018-03-22 15:36:43,249 - __main__ - INFO - doc: file open test 2018-03-22 15:36:43,249 - __main__ - INFO - __enter__:you can add you method 2018-03-22 15:36:43,249 - __main__ - INFO - you can do something in decorator 2018-03-22 15:36:43,249 - __main__ - INFO - @ContextDecorator():testfun test success 2018-03-22 15:36:43,249 - __main__ - INFO - write file success 2018-03-22 15:36:43,249 - __main__ - INFO - __exit__ 2018-03-22 15:36:43,249 - __main__ - INFO - type:None
原文地址：https://www.cnblogs.com/xiaobingqianrui/p/8624306.html
时间： 2024-10-10 10:19:14