How do I use method overloading in Python?

It's method overloading, not method overriding. And in Python, you do it all in one function:

class A:

    def stackoverflow(self, i='some_default_value'):
        print 'only method'

ob=A()
ob.stackoverflow(2)
ob.stackoverflow()

You can't have two methods with the same name in Python -- and you don't need to.

See the Default Argument Values section of the Python tutorial. See "Least Astonishment" and the Mutable Default Argument for a common mistake to avoid.

See PEP 443 for information about the new single dispatch generic functions in Python 3.4.

You can also use pythonlangutil:

from pythonlangutil.overload import Overload, signature

class A:
    @Overload
    @signature()
    def stackoverflow(self):    
        print 'first method'

    @stackoverflow.overload
    @signature("int")
    def stackoverflow(self, i):
        print 'second method', i

In Python, you don't do things that way. When people do that in languages like Java, they generally want a default value (if they don't, they generally want a method with a different name). So, in Python, you can have default values.

class A(object):  # Remember the ``object`` bit when working in Python 2.x

    def stackoverflow(self, i=None):
        if i is None:
            print 'first form'
        else:
            print 'second form'

As you can see, you can use this to trigger separate behaviour rather than merely having a default value.

>>> ob = A()
>>> ob.stackoverflow()
first form
>>> ob.stackoverflow(2)
second form

While agf was right with the answer in the past, now with PEP-3124 we got our syntactic sugar.

See typing documentation for details on the @overload decorator, but note that this is really just syntactic sugar and IMHO this is all people have been arguing about ever since.

Personally, I agree that having multiple functions with different signatures makes it more readable then having a single function with 20+ arguments all set to a default value (None most of the time) and then having to fiddle around using endless if, elif, else chains to find out what the caller actually wants our function to do with the provided set of arguments. This was long overdue following the Python Zen:

Beautiful is better than ugly.

and arguably also

Simple is better than complex.

Straight from the official Python documentation linked above:

from typing import overload
@overload
def process(response: None) -> None:
    ...
@overload
def process(response: int) -> Tuple[int, str]:
    ...
@overload
def process(response: bytes) -> str:
    ...
def process(response):
    <actual implementation>

EDIT: for anyone wondering why this example is not working as you'd expect if from other languages I'd suggest to take a look at this discussion. The @overloaded functions are not supposed to have any actual implementation. This is not obvious from the example in the Python documentation.

How do I use method overloading in Python?

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