# -*- coding: utf-8 -*-
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# Institut Federatif de Recherche 49
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'''Utility functions to make a weak proxy which also keeps an access to its original object reference. :func:`weakref.proxy` doesn't allow this, but functions that check types (C+/Python bindings for instance) cannot work with proxies.
We build such a proxy by setting a :func:`weakref.ref` object in the proxy (actually in the object itself).
'''
from __future__ import absolute_import
import weakref
[docs]def get_ref(obj):
''' Get a regular reference to an object, whether it is already a regular
reference, a weak reference, or a weak proxy which holds an access to the
original reference (built using :func:`weak_proxy`).
In case of a weak proxy not built using :func:`weak_proxy`, we try to get
the ``self`` from a bound method of the object, namely
``obj.__init__.__self__``, if it exists.
'''
if isinstance(obj, weakref.ReferenceType):
return obj()
elif isinstance(obj, weakref.ProxyTypes):
if hasattr(obj, '_weakref'):
return obj._weakref()
elif hasattr(obj, '__init__'):
# try to get the 'self' of a bound method
return obj.__init__.__self__
return obj
[docs]def weak_proxy(obj, callback=None):
''' Build a weak proxy (:class:`weakref.ProxyType`) from an object, if it
is not already one, and keep a reference to the original object (via a
:class:`weakref.ReferenceType`) in it.
*callback* is passed to :func:`weakref.proxy`.
'''
if isinstance(obj, weakref.ProxyTypes):
return obj
real_obj = get_ref(obj)
if callback:
wr = weakref.proxy(real_obj, callback)
else:
wr = weakref.proxy(real_obj)
wr._weakref = weakref.ref(real_obj)
return wr
[docs]class proxy_method(object):
''' Indirect proxy for a bound method
It replaces a bound method, ie ``a.method`` with a proxy callable which
does not take a reference on ``a``.
Especially useful for callbacks.
If we want to set a notifier with a callback on a proxy object (without
adding a new reference on it), we can use proxy_method::
a = anatomist.Anatomist()
a.onCursorNotifier.onAddFirstListener.add(
partial(proxy_method(a, 'enableListening'),
"LinkedCursor", a.onCursorNotifier)))
del a
Without this mechanism, using::
a.onCursorNotifier.onAddFirstListener.add(
partial(a.enableListening, "LinkedCursor", a.onCursorNotifier)))
would increment the reference count on a, because ``a.enableListening``,
as a *bound method*, contains a reference to a, and will prevent the
deletion of ``a`` (here the Anatomist application)
'''
def __init__(self, obj, method=None):
'''
The constructor takes as parameters, either the object and its method
name (as a string), or the bound method itself.
'''
if method is None:
method = obj.__name__
obj = obj.__self__
self.proxy = weak_proxy(obj)
self.method = method
def __call__(self, *args, **kwargs):
return getattr(self.proxy, self.method)(*args, **kwargs)