questions about object references

Ned Deily nad at acm.org
Fri Aug 7 22:41:53 CEST 2009


In article <786181.46665.qm at web110610.mail.gq1.yahoo.com>,
 William <abecedarian314159 at yahoo.com> wrote:

> I have a question.  Suppose I do the following:
> 
> def myfunc(a,b):
>   return a+b
> 
> myfunc2=myfunc
> 
> is there anyway to find all of the references to myfunc?  That is, can I find 
> out all of the functions that may be aliased to myfunc?

The general idea is to search the appropriate namespaces and check for 
object identity, so something like:

>>> def myfunc(a,b):
...     return a+b
... 
>>> myfunc2 = myfunc
>>> 
>>> name = None
>>> namespace = globals()
>>> 
>>> for name in namespace:
...     if namespace[name] is myfunc:
...         print " %s = %s" % (name, namespace[name])
... 
 myfunc = <function myfunc at 0xc2670>
 myfunc2 = <function myfunc at 0xc2670>

> second question:
> 
> class MyClass(object):
>  def __init__(a,b):
>    self.a=a
>    self.b=b
>   def myfunc(self):
>     return self.a+self.b
> 
> myclass=MyClass(3,4)
> myclass.myfunc2=myclass.myfunc
> 
> Is there any way to find all the references to myclass.myfunc--in this case,
> myclass.myfunc2?

This is a little trickier since the object you are searching for is a 
bound method; while it might seem like it should, testing for object 
identity doesn't work.  (You'd could test for identity of the function 
objects pointed to by the bound methods' __func__ attributes.)  However, 
plain old test for equality works, so, for example, to search the 
instance object's attribute space:

>>> class MyClass(object):
...     def __init__(self,a,b):
...         self.a=a
...         self.b=b
...     def myfunc(self):
...         return self.a+self.b
... 
>>> myclass = MyClass(3,4)
>>> myclass.myfunc2 = myclass.myfunc
>>> 
>>> for name in dir(myclass):
...     obj = getattr(myclass, name)  
...     if obj == myclass.myfunc:
...         print " %s is %s" % (name, obj)
... 
 myfunc is <bound method MyClass.myfunc of <__main__.MyClass object at 
0xc6d70>>
 myfunc2 is <bound method MyClass.myfunc of <__main__.MyClass object at 
0xc6d70>>

-- 
 Ned Deily,
 nad at acm.org




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