Every instance method is expected to have at least one positional parameter. This parameter will reference the object instance on which the method
is called. Calling an instance method which doesn’t have at least one parameter will raise a "TypeError". By convention, this first parameter is
usually named "self".
Class methods, i.e. methods annotated with @classmethod, also require at least one parameter. The only differences is that it will
receive the class itself instead of a class instance. By convention, this first parameter is usually named "cls". Note that __new__ and
__init_subclass__ take a class as first argument even thought they are not decorated with @classmethod.
This rule raises an issue when an instance of class method does not have at least one positional parameter.
Noncompliant Code Example
class MyClass:
def instance_method(): # Noncompliant. "self" parameter is missing.
print("instance_method")
@classmethod
def class_method(): # Noncompliant. "cls" parameter is missing.
print("class_method")
Compliant Solution
class MyClass:
def instance_method(self):
print("instance_method")
@classmethod
def class_method(cls):
print("class_method")
@staticmethod
def static_method():
print("static_method")
See
