Only the first argument differs:
- normal method: the current object is automatically passed as an (additional) first argument
- classmethod: the class of the current object is automatically passed as an (additional) fist argument
- staticmethod: no extra arguments are automatically passed. What you passed to the function is what you get.
In more detail...
normal method
The "standard" method, as in every object oriented language. When an object's method is called, it is automatically given an extra argument self as its first argument. That is, method
def f(self, x, y)
must be called with 2 arguments. self is automatically passed, and it is the object itself. Similar to the this that magically appears in eg. java/c++, only in python it is shown explicitly.
actually, the first argument does not have to be called
self, but it's the standard convention, so keep it
class method
When the method is decorated
@classmethod
def f(cls, x, y)
the automatically provided argument is not self, but the class of self.
static method
When the method is decorated
@staticmethod
def f(x, y)
the method is not given any automatic argument at all. It is only given the parameters that it is called with.
usages
classmethodis mostly used for alternative constructors.staticmethoddoes not use the state of the object, or even the structure of the class itself. It could be a function external to a class. It only put inside the class for grouping functions with similar functionality (for example, like Java'sMathclass static methods)
class Point
def __init__(self, x, y):
self.x = x
self.y = y
@classmethod
def frompolar(cls, radius, angle):
"""The `cls` argument is the `Point` class itself"""
return cls(radius * cos(angle), radius * sin(angle))
@staticmethod
def angle(x, y):
"""this could be outside the class, but we put it here
just because we think it is logically related to the class."""
return atan(y, x)
p1 = Point(3, 2)
p2 = Point.frompolar(3, pi/4)
angle = Point.angle(3, 2)
