rspec/rules/S5719/python/rule.adoc

This rule raises an issue when an instance or a class method does not have at least one positional parameter.

== Why is this an issue?

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 they will receive the class itself instead of a class instance. By convention, this first parameter is usually named `cls`. 

=== Exceptions

Static methods (methods annotated with the `@staticmethod` decorator) do not require any positional parameter. This rule will not raise an issue on them.

== How to fix it

Adding `self` as the first parameter of an instance method or `cls` as the first parameter of a class method will resolve the issue.

=== Code examples

==== Noncompliant code example

[source,python,diff-id=1,diff-type=noncompliant]
----
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

[source,python,diff-id=1,diff-type=compliant]
----
class MyClass:
    def instance_method(self):
        print("instance_method")

    @classmethod
    def class_method(cls):
        print("class_method")

    @staticmethod
    def static_method():
        print("static_method")
----

=== Pitfalls

Note that ``++__new__++`` and ``++__init_subclass__++`` take a class as first argument even thought they are not decorated with `@classmethod`.

== Resources

=== Documentation

* https://docs.python.org/3.11/tutorial/classes.html#method-objects[Method Objects] - Python Method Objects
* https://docs.python.org/3.11/library/functions.html?highlight=classmethod#classmethod[Class Method] - Python Class Method 

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Method has no @classmethod or @staticmethod annotation

* Add a "self" or class parameter

Method has a @classmethod annotation, or method is __new__ or __init_subclass__

* Add a class parameter


=== Highlighting

The method signature ``++def name()++``


endif::env-github,rspecator-view[]