16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
79 lines
1.8 KiB
Plaintext
79 lines
1.8 KiB
Plaintext
== Why is this an issue?
|
|
|
|
:link-with-uscores1: https://docs.python.org/3/reference/datamodel.html#object.__len__
|
|
|
|
The {link-with-uscores1}[``++__len__++``] special method enables to define the length of an object. As such it should always return an integer greater than or equal to 0. When the ``++len(...)++`` builtin is called on an object, any other return type will raise a ``++TypeError++`` and a negative integer will raise a ``++ValueError++``.
|
|
|
|
|
|
This rule raises an issue when a ``++__len__++`` method returns an expression which is not an integer greater than or equal to 0.
|
|
|
|
|
|
=== Noncompliant code example
|
|
|
|
[source,python]
|
|
----
|
|
class A:
|
|
def __len__(self):
|
|
return 2.0 # Noncompliant
|
|
|
|
len(A()) # This will raise "TypeError: 'float' object cannot be interpreted as an integer"
|
|
|
|
class B:
|
|
def __len__(self):
|
|
return -2 # Noncompliant
|
|
|
|
len(B()) # This will raise "ValueError: __len__() should return >= 0"
|
|
----
|
|
|
|
|
|
=== Compliant solution
|
|
|
|
[source,python]
|
|
----
|
|
class A:
|
|
def __len__(self):
|
|
return 2
|
|
|
|
len(A()) # This will return 2
|
|
----
|
|
|
|
|
|
:link-with-uscores1: https://docs.python.org/3/reference/datamodel.html#object.__index__
|
|
|
|
=== Exceptions
|
|
|
|
This rule raises no issue when the type returned by ``++__len__++`` is a class implementing the {link-with-uscores1}[``++__index__++``] special method.
|
|
|
|
|
|
[source,python]
|
|
----
|
|
class Ind:
|
|
def __index__(self):
|
|
return 3
|
|
|
|
class A:
|
|
def __len__(self):
|
|
return Ind()
|
|
|
|
len(A()) # This will return 3
|
|
----
|
|
|
|
ifdef::env-github,rspecator-view[]
|
|
|
|
'''
|
|
== Implementation Specification
|
|
(visible only on this page)
|
|
|
|
=== Message
|
|
|
|
* Replace this return value with an integer >= 0; XXX is negative.
|
|
* Replace this return value with an integer >= 0; XXX is of type YYY.
|
|
|
|
|
|
=== Highlighting
|
|
|
|
Primary: The returned expression
|
|
|
|
|
|
endif::env-github,rspecator-view[]
|