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# ====================================================================
# Provides a with-style resource handler for optionally-None resources
# ====================================================================
class optional_with(object):
# pylint: disable=too-few-public-methods
# This is a wrapper - it is not meant to provide any extra methods.
"""Provides a wrapper for objects supporting "with", allowing None.
This lets a user use the "with object" syntax for resource usage
(e.g. locks) even when the wrapped with object is None.
e.g.
wrapped_lock = optional_with(thread.Lock())
with wrapped_lock:
# Do something while the lock is obtained.
pass
might_be_none = None
wrapped_none = optional_with(might_be_none)
with wrapped_none:
# This code here still works.
pass
This prevents having to write code like this when
a lock is optional:
if lock:
lock.acquire()
try:
code_fragment_always_run()
finally:
if lock:
lock.release()
And I'd posit it is safer, as it becomes impossible to
forget the try/finally using optional_with(), since
the with syntax can be used.
"""
def __init__(self, wrapped_object):
self.wrapped_object = wrapped_object
def __enter__(self):
if self.wrapped_object is not None:
return self.wrapped_object.__enter__()
else:
return self
def __exit__(self, the_type, value, traceback):
if self.wrapped_object is not None:
return self.wrapped_object.__exit__(the_type, value, traceback)
else:
# Don't suppress any exceptions
return False
|
