Looping over a Python / IronPython Object Methods

Question

What is the proper way to loop over a Python object's methods and call them?

Given the object:

class SomeTest():
  def something1(self):
    print "something 1"
  def something2(self):
    print "something 2"

Answer 1

You can use the inspect module to get class (or instance) members:

>>> class C(object):
...     a = 'blah'
...     def b(self):
...             pass
... 
...
>>> c = C()
>>> inspect.getmembers(c, inspect.ismethod)
[('b', <bound method C.b of <__main__.C object at 0x100498250>>)]

getmembers() returns a list of tuples, where each tuple is (name, member). The second argument to getmembers() is the predicate, which filters the return list (in this case, returning only method objects)

Answer 2

Methods vs. functions and other types of callables...

(To address the issue in the comments in Unknown's post.)

First, it should be noted that, in addition to user-defined methods, there are built-in methods, and a built-in method is, as the doc at http://docs.python.org/reference/datamodel.html says, "really a different disguise of a built-in function" (which is a wrapper around a C function.)

As for user-defined methods, as Unknown's cited quote says:

A user-defined method object combines a class, a class instance (or None) and any callable object (normally a user-defined function).

But this does not mean that "anything that defines __call__ and is attached to an object is a method." A method is a callable, but a callable is not necessarily a method. User-defined methods are wrappers around what the quote says.

Hopefully this output (from Python 2.5.2 which I have handy) will show the distinction:

IDLE 1.2.2      
>>> class A(object):
    x = 7


>>> A  # show the class object
<class '__main__.A'>
>>> a = A()
>>> a  # show the instance
<__main__.A object at 0x021AFBF0>
>>> def test_func(self):
    print self.x


>>> type(test_func)  # what type is it?
<type 'function'>
>>> dir(test_func)  # what does it have?
['__call__', '__class__', '__delattr__', '__dict__', '__doc__', '__get__',
 '__getattribute__', '__hash__', '__init__', '__module__', '__name__',
 '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__',
 '__str__', 'func_closure', 'func_code', 'func_defaults', 'func_dict',
 'func_doc', 'func_globals', 'func_name']
>>> # But now let's put test_func on the class...
>>> A.test = test_func
>>> type(A.test)  # What type does this show?
<type 'instancemethod'>
>>> dir(A.test)  # And what does it have?
['__call__', '__class__', '__cmp__', '__delattr__', '__doc__', '__get__',
 '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__',
 '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'im_class',
 'im_func', 'im_self']
>>> # See, we just got a wrapper, and the function is in 'im_func'...
>>> getattr(A.test, 'im_func')
<function test_func at 0x0219F4B0>
>>> # Now to show bound vs. unbound methods...
>>> getattr(a.test, 'im_self') # Accessing it via the instance
<__main__.A object at 0x021AFBF0>
>>> # The instance is itself 'im_self'
>>> a.test()
7
>>> getattr(A.test, 'im_self') # Accessing it via the class returns None...
>>> print getattr(A.test, 'im_self')
None
>>> # It's unbound when accessed that way, so there's no instance in there
>>> # Which is why the following fails...
>>> A.test()

Traceback (most recent call last):
  File "<pyshell#25>", line 1, in <module>
    A.test()
TypeError: unbound method test_func() must be called with A instance as
first argument (got nothing instead)
>>>

And - editing to add the following additional output, which is also relevant...

>>> class B(object):
    pass

>>> b = B()
>>> b.test = test_func  # Putting the function on the instance, not class
>>> type(b.test)
<type 'function'>
>>> 

I wont add more output, but you could also make a class an attribute of another class or instance, and, even though classes are callable, you would not get a method. Methods are implemented using non-data descriptors, so look up descriptors if you want more info on how they work.

Answer 3

This code snippet will call anything it will find in obj and store results in mapping, where key is attribute name — dict((k, v()) for (k, v) in obj.__dict__.iteritems() if k.startswith('something'))

Answer 4

Edit

Daniel, you are wrong.

http://docs.python.org/reference/datamodel.html

User-defined methods

A user-defined method object combines a class, a class instance (or None) and any callable object (normally a user-defined function).

Therefore, anything that defines __call__ and is attached to an object is a method.

Answer

The proper way to see what elements an object has is to use the dir() function.

Obviously this example only works for functions that take no arguments.

a=SomeTest()
for varname in dir(a):
    var = getattr(a, varname)
    if hasattr(var, "__call__"):
        var()