rspec/rules/S5655/python/rule.adoc

This rule raises an issue when a function or method is called with an argument of a different type than the one described in its type annotations.

== Why is this an issue?

The CPython interpreter does not check types of arguments when functions are called. 
However, a function can express the type it expects for each argument in its documentation or 
by using https://www.python.org/dev/peps/pep-0484/[Type Hints]. 
While the code may initially work as intended, not respecting the contract of an API may lead to bugs later 
when its implementation evolves or when type checks are added (i.e. with `isinstance`).

This rule also checks argument types for built-in functions.

=== Noncompliant code example

[source,python,diff-id=1,diff-type=noncompliant]
----
def func(var: str):
    pass

func(42)  # Noncompliant: 42 is not of type str.

round("not a number")  # Noncompliant: the builtin function round requires a number as first parameter.
----


=== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
def func(var: str):
    pass

func("42")

round(1.2)
----


== Resources

=== Documentation 

* Python documentation - https://docs.python.org/3/library/functions.html#built-in-funcs[builtins]
* Python documentation - https://docs.python.org/3/library/typing.html[typing — Support for type hints]
* PEP 484 - https://www.python.org/dev/peps/pep-0484/[Type Hints]

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

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

=== Message

* Change this argument of type XXX; Function FFF expects type YYY


=== Highlighting

Primary: the expression provided as argument

Secondary:

* location: definition of the function called
* message: "Function definition"


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