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Python

"""
Module for testing automatic garbage collection of objects
.. autosummary::
:toctree: generated/
set_gc_state - enable or disable garbage collection
gc_state - context manager for given state of garbage collector
assert_deallocated - context manager to check for circular references on object
"""
import weakref
import gc
import sys
from contextlib import contextmanager
__all__ = ['set_gc_state', 'gc_state', 'assert_deallocated']
IS_PYPY = '__pypy__' in sys.modules
class ReferenceError(AssertionError):
pass
def set_gc_state(state):
""" Set status of garbage collector """
if gc.isenabled() == state:
return
if state:
gc.enable()
else:
gc.disable()
@contextmanager
def gc_state(state):
""" Context manager to set state of garbage collector to `state`
Parameters
----------
state : bool
True for gc enabled, False for disabled
Examples
--------
>>> with gc_state(False):
... assert not gc.isenabled()
>>> with gc_state(True):
... assert gc.isenabled()
"""
orig_state = gc.isenabled()
set_gc_state(state)
yield
set_gc_state(orig_state)
@contextmanager
def assert_deallocated(func, *args, **kwargs):
"""Context manager to check that object is deallocated
This is useful for checking that an object can be freed directly by
reference counting, without requiring gc to break reference cycles.
GC is disabled inside the context manager.
This check is not available on PyPy.
Parameters
----------
func : callable
Callable to create object to check
\\*args : sequence
positional arguments to `func` in order to create object to check
\\*\\*kwargs : dict
keyword arguments to `func` in order to create object to check
Examples
--------
>>> class C(object): pass
>>> with assert_deallocated(C) as c:
... # do something
... del c
>>> class C(object):
... def __init__(self):
... self._circular = self # Make circular reference
>>> with assert_deallocated(C) as c: #doctest: +IGNORE_EXCEPTION_DETAIL
... # do something
... del c
Traceback (most recent call last):
...
ReferenceError: Remaining reference(s) to object
"""
if IS_PYPY:
raise RuntimeError("assert_deallocated is unavailable on PyPy")
with gc_state(False):
obj = func(*args, **kwargs)
ref = weakref.ref(obj)
yield obj
del obj
if ref() is not None:
raise ReferenceError("Remaining reference(s) to object")