__init__ and arguments in Python
In Python:
- Instance methods: require the
self
argument. - Class methods: take the class as a first argument.
- Static methods: do not require either the instance (
self
) or the class (cls
) argument.
__init__
is a special function and without overriding __new__
it will always be given the instance of the class as its first argument.
An example using the builtin classmethod and staticmethod decorators:
import sys
class Num:
max = sys.maxint
def __init__(self,num):
self.n = num
def getn(self):
return self.n
@staticmethod
def getone():
return 1
@classmethod
def getmax(cls):
return cls.max
myObj = Num(3)
# with the appropriate decorator these should work fine
myObj.getone()
myObj.getmax()
myObj.getn()
That said, I would try to use @classmethod
/@staticmethod
sparingly. If you find yourself creating objects that consist of nothing but staticmethod
s the more pythonic thing to do would be to create a new module of related functions.
Every method needs to accept one argument: The instance itself (or the class if it is a static method).
Read more about classes in Python.
The fact that your method does not use the self
argument (which is a reference to the instance that the method is attached to) doesn't mean you can leave it out. It always has to be there, because Python is always going to try to pass it in.