CODEWITHSUNDEEP
pythonclass
Psyduck
Psyduck

Reputation: 667

Calling method, classmethod, staticmethod in the same Python class

From a famous example, I learned the difference between method, classmethod and staticmethod in a Python class.

Source: What is the difference between @staticmethod and @classmethod in Python?

class A(object):
    def foo(self,x):
        print "executing foo(%s,%s)"%(self,x)

    @classmethod
    def class_foo(cls,x):
        print "executing class_foo(%s,%s)"%(cls,x)

    @staticmethod
    def static_foo(x):
        print "executing static_foo(%s)"%x   
    # My Guesses
    def My_Question(self,x):
        self.foo(x)
        A.class_foo(x)
        A.static_foo(x)

a=A()

Now I am wondering, how to call a method, @classmethod, and @staticmethod inside the class.

I put my guesses in the My_Question function above, please correct me if I am wrong with any of these.

Upvotes: 4

Views: 2793

Answers (2)

mgilson
mgilson

Reputation: 309929

Yes, your guesses will work. Note that it is also possible/normal to call staticmethods and classmethods outside the class:

class A():
    ...

A.class_foo()
A.static_foo()

Also note that inside regular instance methods, it's customary to call the staticmethods and class methods directly on the instance (self) rather than the class (A):

class A():
    def instance_method(self):
        self.class_foo()
        self.static_foo()

This allow for inheritance to work as you might expect -- If I create a B subclass from A, if I call B.instance_method(), my class_foo function will get B instead of A as the cls argument -- And possibly, if I override static_foo on B to do something slightly different than A.static_foo, this will allow the overridden version to be called as well.

Some examples might make this more clear:

class A(object):
    @staticmethod
    def static():
        print("Static, in A")

    @staticmethod
    def staticoverride():
        print("Static, in A, overrideable")

    @classmethod
    def clsmethod(cls):
        print("class, in A", cls)

    @classmethod
    def clsmethodoverrideable(cls):
        print("class, in A, overridable", cls)

    def instance_method(self):
        self.static()
        self.staticoverride()
        self.clsmethod()
        self.clsmethodoverride()

class B(A):
    @classmethod
    def clsmethodoverrideable(cls):
        print("class, in B, overridable", cls)

    @staticmethod
    def staticoverride():
        print("Static, in B, overrideable")


a = A()
b = B()
a.instance_method()
b.instance_method()

...

After you've run that, try it by changing all of the self. to A. inside instance_method. Rerun and compare. You'll see that all of the references to B have gone (even when you're calling b.instance_method()). This is why you want to use self rather than the class.

Upvotes: 2

araraonline
araraonline

Reputation: 1562

As @wim said, what you have is right. Here's the output when My_Question is called.

>>> a.My_Question("My_Answer=D")
executing foo(<__main__.A object at 0x0000015790FF4668>,My_Answer=D)
executing class_foo(<class '__main__.A'>,My_Answer=D)
executing static_foo(My_Answer=D)

Upvotes: 1

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