Static Class Methods
Types of Methods#
Static Method#
In other programming languages like php you can create a static method
class MyClass {
public static function times2($input) {
return $input * 2;
}
}
echo MyClass::times2(40);
So static methods can be called without creating an instance / object first.
In python it is similar but it uses the @staticmethod decorator.
Also they do not take a self or cls argument.
class MyClass:
@staticmethod
def staticmethod():
"""
Static methods don't have access to `cls` or `self`.
They work like regular functions but belong to
the class's namespace.
"""
return 'static method called'
def method(self):
"""
Instance methods need a class instance and
can access the instance through `self`.
"""
return 'instance method called', self
Class Methods#
Class methods are similar to instance methods, but they differ in that an instance need not be created.
Ie. they can be called without an instance. They do require the cls as an argument which is not the instance but the actual class or blueprint for creating objects.
With a classmethod you don’t call __init__ you call cls()
Class methods allow for inheritance among classes - not objects.
class MyClass:
@classmethod
def classmethod(cls):
"""
Class methods don't need a class instance.
They can't access the instance (self) but
they have access to the class itself via `cls`.
"""
return 'class method called', cls
The standard instance method#
class MyClass:
def method(self):
"""
Instance methods need a class instance and
can access the instance through `self`.
"""
return 'instance method called', self
Calling the methods#
# All methods types can be
# called on a class instance:
>>> obj = MyClass()
>>> obj.method()
('instance method called', <MyClass instance at 0x1019381b8>)
>>> obj.classmethod()
('class method called', <class MyClass at 0x101a2f4c8>)
>>> obj.staticmethod()
'static method called'
# Calling instance methods fails
# if we only have the class object:
>>> MyClass.classmethod()
('class method called', <class MyClass at 0x101a2f4c8>)
>>> MyClass.staticmethod()
'static method called'
>>> MyClass.method()
TypeError:
"unbound method method() must be called with MyClass "
"instance as first argument (got nothing instead)"