# -*- coding: utf-8 -*-
import new
from weakref import ref
class WeakCallableRef( object ):
 u"""
 Implements a weakref for callables, be they functions or methods.
 Due to implementation details, native Python weakrefs on bound methods always
 expire right away. WeakCallableRef, on the other hand, only expires bound
 method references when the object the method is bound to expires. It
 otherwise behaves like native Python weakref for other callables (functions
 and static methods).
 To demonstrate, let's create callables of all three kinds:
>>> def test1():
 ... pass
>>> class TestClass:
 ... def test2( self ): pass
 ... @staticmethod
 ... def test3(): pass
>>> test_obj = TestClass()
 And a little function to tell us when a ref is deleted:
>>> def call_on_expire( ref ):
 ... print "Deleted %r!" % ref
 Ok. And now, let's create the weakrefs.
>>> func_ref = WeakCallableRef( test1, call_on_expire )
>>> bound_meth_ref = WeakCallableRef( test_obj.test2, call_on_expire )
>>> static_meth_ref = WeakCallableRef( TestClass.test3, call_on_expire )
 The original callable can be retrieved by calling the weakref:
>>> print func_ref()
 <function test1 at ...>
>>> print bound_meth_ref()
 <bound method TestClass.test2 ...>
>>> print static_meth_ref()
 <function test3 ...>
 When the original callable disappears, the notification function is
 triggered.
>>> del test1
 Deleted <...weakcallableref...(test1)...>!
>>> del test_obj
 Deleted <...weakcallableref...(test2)...>!
>>> del TestClass
 Deleted <...weakcallableref...(test3)...>!
 And if called, the weakrefs must now return None:
>>> print func_ref(), bound_meth_ref(), static_meth_ref()
 None None None
 """
 def __init__( self, fn, callback=None ):
 assert callable( fn )
 self._objref = None
 self._fnref = None
 self._class = None
 self._dead = False
 self._callback = callback
 self._fnname = ""
 obj = getattr( fn, "im_self", None )
 if obj is not None: ## fn is a bound method
 self._objref = ref( obj, self.markDead )
 self._fnref = ref( fn.im_func, self.markDead )
 self._class = fn.im_class
 self._fnname = fn.im_func.func_name
 else: ## fn is a static method or a plain function
 self._fnref = ref( fn, self.markDead )
 self._fnname = fn.func_name
 def markDead( self, objref ):
 if not self._dead:
 callback = self._callback
 self._dead = True
 self._objref = None
 self._fnref = None
 self._class = None
 self._callback = None
 if callback:
 return callback( self )
 def __call__( self ):
 if self._objref: ## bound method
 ## Bind the method on the fly, and return it.
 fn = self._fnref()
 obj = self._objref()
 if None in ( fn, obj ):
 return None
 return new.instancemethod( fn, obj, self._class )
 elif self._fnref:
 return self._fnref()
 else:
 return None
 def __repr__( self ):
 return "<%s instance at %s (%s)%s>" % (
 self.__class__,
 hex( id( self ) ),
 self._fnname,
 self._dead and "; dead" or ""
 )
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