Python does not check returned types by default, however some methods are expected to return a specific type otherwise builtin functions will fail.


This rule raises an issue when a builtin function or method:

* does not return a value of the expected type.
* returns a value when no value should be returned.
* returns no value when a return value is expected.

In such way that the resulting code would result in a runtime error.

== Noncompliant Code Example

----
class MyInt:
    def __init__(self):
        return self  # Noncompliant. __init__ should return nothing. This will raise a TypeError.

    def __int__(self):
        return 3.0  # Noncompliant. __int__ should always return an integer

int(MyInt())  # This will fail with "TypeError: __int__ returned non-int (type float)"
----

== Compliant Solution

----
class MyInt:
    def __int__(self):
        return 3

int(MyInt())
----

== See

* https://docs.python.org/3/reference/datamodel.html#special-method-names[Python documentation - Special method names]

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