How can one check if a variable is an instance method or not? I'm using python 2.5.
Something like this:
class Test:
def method(self):
pass
assert is_instance_method(Test().method)
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18What's wrong with asking here?quano– quano2009-08-11 13:52:14 +00:00Commented Aug 11, 2009 at 13:52
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3Reading the source isn't any help - presumably he's writing some code that needs to know the answer at runtime. Possibly iterating through all attrs on an object, for instance.Jonathan Hartley– Jonathan Hartley2010-05-24 16:01:35 +00:00Commented May 24, 2010 at 16:01
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2 Answers
inspect.ismethod is what you want to find out if you definitely have a method, rather than just something you can call.
import inspect
def foo(): pass
class Test(object):
def method(self): pass
print inspect.ismethod(foo) # False
print inspect.ismethod(Test) # False
print inspect.ismethod(Test.method) # True
print inspect.ismethod(Test().method) # True
print callable(foo) # True
print callable(Test) # True
print callable(Test.method) # True
print callable(Test().method) # True
callable is true if the argument if the argument is a method, a function (including lambdas), an instance with __call__ or a class.
Methods have different properties than functions (like im_class and im_self). So you want
assert inspect.ismethod(Test().method)
3 Comments
Alex Martelli
+1, inspect is good (and that "defiantly" typo actually reads well;-).
Devin
Using Python 3.5,
inspect.ismethod(Test.method) returns False.
Andreas
You should use an instance of test sinse it is an instance method ``` inspect.ismethod(Test().method) ```
If you want to know if it is precisely an instance method use the following function. (It considers methods that are defined on a metaclass and accessed on a class class methods, although they could also be considered instance methods)
import types
def is_instance_method(obj):
"""Checks if an object is a bound method on an instance."""
if not isinstance(obj, types.MethodType):
return False # Not a method
if obj.im_self is None:
return False # Method is not bound
if issubclass(obj.im_class, type) or obj.im_class is types.ClassType:
return False # Method is a classmethod
return True
Usually checking for that is a bad idea. It is more flexible to be able to use any callable() interchangeably with methods.
