mirror of
https://github.com/python/cpython.git
synced 2024-11-23 18:04:37 +08:00
b940e113bf
(a) "except E, V" -> "except E as V" (b) V is now limited to a simple name (local variable) (c) V is now deleted at the end of the except block
155 lines
4.0 KiB
Python
155 lines
4.0 KiB
Python
"""Utilities for with-statement contexts. See PEP 343."""
|
|
|
|
import sys
|
|
|
|
__all__ = ["contextmanager", "nested", "closing"]
|
|
|
|
class GeneratorContextManager(object):
|
|
"""Helper for @contextmanager decorator."""
|
|
|
|
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)
|
|
raise RuntimeError("generator didn't stop after throw()")
|
|
except StopIteration as exc:
|
|
# 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
|
|
return exc is not value
|
|
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>
|
|
|
|
"""
|
|
def helper(*args, **kwds):
|
|
return GeneratorContextManager(func(*args, **kwds))
|
|
try:
|
|
helper.__name__ = func.__name__
|
|
helper.__doc__ = func.__doc__
|
|
helper.__dict__ = func.__dict__
|
|
except:
|
|
pass
|
|
return helper
|
|
|
|
|
|
@contextmanager
|
|
def nested(*managers):
|
|
"""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 = []
|
|
exc = (None, None, None)
|
|
try:
|
|
try:
|
|
for mgr in managers:
|
|
exit = mgr.__exit__
|
|
enter = mgr.__enter__
|
|
vars.append(enter())
|
|
exits.append(exit)
|
|
yield vars
|
|
except:
|
|
exc = sys.exc_info()
|
|
finally:
|
|
while exits:
|
|
exit = exits.pop()
|
|
try:
|
|
if exit(*exc):
|
|
exc = (None, None, None)
|
|
except:
|
|
exc = sys.exc_info()
|
|
if exc != (None, None, None):
|
|
# 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]
|
|
|
|
|
|
class closing(object):
|
|
"""Context to automatically close something at the end of a block.
|
|
|
|
Code like this:
|
|
|
|
with closing(<module>.open(<arguments>)) as f:
|
|
<block>
|
|
|
|
is equivalent to this:
|
|
|
|
f = <module>.open(<arguments>)
|
|
try:
|
|
<block>
|
|
finally:
|
|
f.close()
|
|
|
|
"""
|
|
def __init__(self, thing):
|
|
self.thing = thing
|
|
def __enter__(self):
|
|
return self.thing
|
|
def __exit__(self, *exc_info):
|
|
self.thing.close()
|