class method vs static method

[Chris Brat]

Hi,

I've done some reading up but I cant get my head around how/why class
methods can be used as apposed to static methods.

Can anyone give an example of where they have used class methods?

Thanks,
Chris

 

[Marc 'BlackJack' Rintsch]

I've done some reading up but I cant get my head around how/why class
methods can be used as apposed to static methods.

Can anyone give an example of where they have used class methods?

----
class Spam(object):
def __init__(self, data):
self.data = data

@classmethod
def load(cls, filename):
# Open file and load data.
data = 'eric'
return cls(data)

class Ham(Spam):
pass

ham = Ham.load('test.dat')
print type(ham)
----

Here the type of `ham` is ``<class '__main__.Ham'>`` because a class
method will receive the class on which the method is called as first
argument. In a static method you don't know if it is called on the class
where the method is defined or on a subclass.

Ciao,
Marc 'BlackJack' Rintsch

 

[Michele Simionato]

Hi,

I've done some reading up but I cant get my head around how/why class
methods can be used as apposed to static methods.

Can anyone give an example of where they have used class methods?

Thanks,
Chris

Class methods are typically used as factories:

class MyClass(object):
@classmethod
def myfactory(cls):
self = cls()
initialize(self)
return self

With different factories you can obtain instances of the same classes
initialized in different ways. This is probably better than writing a
lot of subclasses
with different __init__s. This is my typical use case, but I am sure
others will post
many other examples of application.

Michele Simionato

 

[Bruno Desthuilliers]

Hi,

I've done some reading up but I cant get my head around how/why class
methods can be used as apposed to static methods.

a "static method" is actually not much more than a plain function
living in a class's namespace. classmethods, OTOH, have access to the
class object.

Can anyone give an example of where they have used class methods?

The canonical use case is factory methods, but you'll typically find
other possible applications in frameworks.

 

[Chris Brat]

Thanks for the responses - things are clearer now.