Why use staticmethod instead of no decorator at all

Question

There are several good explanations on SO about why/when you should use a class method vs a static method, but I've not been able to find an answer for when you would use a static method over no decoration at all. Consider this

class Foo(object): @staticmethod def f_static(x): print("static version of f, x={0}".format(x)) def f_standalone(x): print("standalone verion of f, x={0}".format(x))

And some output:

>>> F = Foo >>> f = F() >>> F.f_static(5) static version of f, x=5 >>> F.f_standalone(5) standalone verion of f, x=5 >>> f.f_static(5) static version of f, x=5 >>> f.f_standalone(5) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: f_standalone() takes 1 positional argument but 2 were given

From what I've read on here, the primary reason for using staticmethod is basically to keep conceptually similar things together. From the example above, it seems like both solutions do that. The only drawback is that you don't appear to be able to call the non-staticmethod from an instance. Maybe I'm too used to other programming languages, but this does not bother me so much; it's always surprising that I can call class-level stuff from am instance in Python.

So, is this basically the only difference between the two? Or am I missing other benefits? Thanks

"The only drawback is that you don't appear to be able to call the non-staticmethod from an instance" - so, obviously, you've found the reason why the decorator exists. It's to make static methods behave as they do in other languages. (As well as help communicate the how the method is meant to be called.) Just because it's not of benefit to you doesn't mean it's not a valid rationale. — millimoose
– millimoose, Commented Mar 10, 2013 at 0:21
" It's to make static methods behave as they do in other languages". You cannot call a static method from an instance in Java. Objective-C does not have static methods in this sense per se, but you cannot call class methods from an obj-c instance. — D.C.
– D.C., Commented Mar 10, 2013 at 0:24
In Java, you certainly can call a static method via an instance: ideone.com/Gslfp0 (That is, syntactically, I believe the compiler still just resolves it as a call to a static method on the type of said variable but am too lazy to test.) I'd argue this is the primary distinction between "static" methods and "class" methods that Python was going for. — millimoose
– millimoose, Commented Mar 10, 2013 at 0:29
Also, on a more personal note, if I saw a signature like you use on f_standalone(), my first thought wouldn't be "oh, that must be a class method", but "why is he using x and not self?!". — millimoose
– millimoose, Commented Mar 10, 2013 at 0:33
Not really, I was just assuming that knowledge. (It's kind of what I meant by "it makes static methods behave as in other languages" - in that the call works correctly whether it's through a class or an instance.) — millimoose
– millimoose, Commented Mar 10, 2013 at 1:05

Danica · Accepted Answer · 2013-03-10 00:28:05Z

You seem to be using python 3. In python 2:

In [1]: class Foo(object): ...: def f_standalone(x): ...: print("standalone version of f, x={}".format(x)) ...: In [2]: Foo.f_standalone(12) --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-2-2d315c006153> in <module>() ----> 1 Foo.f_standalone(12) TypeError: unbound method f_standalone() must be called with Foo instance as first argument (got int instance instead)

In python 3, you missed another strange use case:

In [1]: class Foo(object): ...: def f_standalone(x): ...: print("standalone version of f, x={}".format(x)) ...: @staticmethod ...: def f_static(x): ...: print("static version of f, x={}".format(x)) ...: In [2]: Foo().f_standalone() standalone version of f, x=<__main__.Foo object at 0x1064daa10> In [3]: Foo().f_static() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-3-addf9c3f2477> in <module>() ----> 1 Foo().f_static() TypeError: f_static() missing 1 required positional argument: 'x'

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