rspec/rules/S5720/python/rule.adoc

Instance methods, i.e. methods not annotated with ``++@classmethod++`` or ``++@staticmethod++``, are expected to have at least one parameter. This parameter will reference the object instance on which the method is called. By convention, this first parameter is named "self".


Naming the "self" parameter differently is confusing. It might also indicate that the "self" parameter was forgotten, in which case calling the method will most probably fail.


Note also that creating methods which are used as static methods without the ``++@staticmethod++`` decorator is a bad practice because calling these methods on an instance will raise a ``++TypeError++``. Either move the method out of the class or decorate it with ``++@staticmethod++``.


This rule raises an issue when the first parameter of an instance method is not called "self".


== Noncompliant Code Example

----
class MyClass:
    def send_request(request):  # Noncompliant. "self" was probably forgotten
        print("send_request")

class ClassWithStaticMethod:
    def static_method(param):  # Noncompliant
        print(param)
ClassWithStaticMethod().static_method(42)  # Method is available on the instance but calling it will raise a TypeError
----


== Compliant Solution

----
class MyClass:
    def send_request(self, request):
        print("send_request")

class ClassWithStaticMethod:
    @staticmethod
    def static_method(param):
        print(param)
ClassWithStaticMethod().static_method(42)
----


== Exceptions

This rule will also accept "cls" or "mcs" as first parameter's name for metaclasses' methods.


No issue will be raised for methods called ``++__init_subclass__++``, ``++__class_getitem__++`` or ``++__new__++`` as these methods' first parameter is a class.


You can also disable issues on methods decorated with a specific decorator. Add these decorators to this rule's "ignoreDecorators" parameter.


With "ignoredDecorators" set to "abstractmethod"

----
from abc import abstractmethod, ABC

class MyClass(ABC):
    @abstractmethod
    def method():  # No issue, even if it is better in this case to also decorate with @staticmethod
        pass
----


== See

* Python documentation - https://docs.python.org/3.8/tutorial/classes.html#method-objects[Method Objects]
* PEP8 - https://www.python.org/dev/peps/pep-0008/#function-and-method-arguments[Function and Method Arguments]


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