Source code for soma.utils.weak_proxy

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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