Know if a object member is a method

Steven D'Aprano steven at REMOVE.THIS.cybersource.com.au
Mon Sep 1 11:16:56 CEST 2008


On Mon, 01 Sep 2008 10:43:25 +0200, Luca wrote:

> Hi all.
> 
> I think this is a newbie question... what is the best method to know if
> a property of an object is a function?
> 
> I'm thinking something as
> 
> if type(obj.methodName)==???
> 
> Can someone help me?

That's not quite as easy as you might think. In my testing, calling 
type(obj.methodName) can give any of the following:

<type 'instancemethod'>
<type 'function'>
<type 'builtin_function_or_method'>


There may be others as well.

Possibly all you really need is to check if the attribute is callable 
without caring what type of method or function it is:

>>> callable(obj.methodName)
True

In my opinion, that's the best way.


If you are sure that the method won't have side-effects or bugs:

>>> try:
...     obj.method()
... except:
...     print "Not a method"
...

(But how can you be sure?)


If you insist on an explicit test, try this:

import new
type(obj.methodName) == new.instancemethod


or alternatively:

>>> isinstance(obj.methodName, new.instancemethod)
True




-- 
Steven



More information about the Python-list mailing list