60 lines
2.3 KiB
Plaintext
60 lines
2.3 KiB
Plaintext
This rule raises an issue when a class derives from one of the following exception classes: ``++BaseException++``, ``++KeyboardInterrupt++``, ``++SystemExit++`` or ``++GeneratorExit++``.
|
||
|
||
== Why is this an issue?
|
||
|
||
https://docs.python.org/3/library/exceptions.html#SystemExit[``++SystemExit++``] is raised when https://docs.python.org/3/library/sys.html#sys.exit[``++sys.exit()++``] is called. https://docs.python.org/3/library/exceptions.html#KeyboardInterrupt[``++KeyboardInterrupt++``] is raised when the user asks the program to stop by pressing interrupt keys. Both exceptions are expected to propagate up until the application stops.
|
||
|
||
In order to avoid catching ``++SystemExit++`` and ``++KeyboardInterrupt++`` by mistake, https://www.python.org/dev/peps/pep-0352/#exception-hierarchy[PEP-352] created the root class ``++BaseException++`` from which ``++SystemExit++``, ``++KeyboardInterrupt++`` and ``++Exception++`` derive. Thus developers can use ``++except Exception:++`` without preventing the software from stopping.
|
||
|
||
The ``++GeneratorExit++`` class also derives from ``++BaseException++`` as it is not really an error and is not supposed to be caught by user code.
|
||
|
||
As said in https://docs.python.org/3/library/exceptions.html#BaseException[Python's documentation], user-defined exceptions are not supposed to inherit directly from ``++BaseException++``. They should instead inherit from ``++Exception++`` or one of its subclasses.
|
||
|
||
=== Code examples
|
||
|
||
==== Noncompliant code example
|
||
|
||
[source,python,diff-id=1,diff-type=noncompliant]
|
||
----
|
||
class MyException(BaseException): # Noncompliant
|
||
pass
|
||
----
|
||
|
||
==== Compliant solution
|
||
|
||
[source,python,diff-id=1,diff-type=compliant]
|
||
----
|
||
class MyException(Exception):
|
||
pass
|
||
----
|
||
|
||
== Resources
|
||
|
||
=== Documentation
|
||
|
||
* PEP 352 – https://www.python.org/dev/peps/pep-0352/#exception-hierarchy-changes[Required Superclass for Exceptions]
|
||
* Python Documentation - https://docs.python.org/3/library/exceptions.html#BaseException[BaseException class]
|
||
|
||
ifdef::env-github,rspecator-view[]
|
||
|
||
'''
|
||
== Implementation Specification
|
||
(visible only on this page)
|
||
|
||
=== Message
|
||
|
||
Derive this class from "Exception" instead of BaseException/GeneratorExit/KeyboardInterrupt/SystemExit
|
||
|
||
|
||
=== Highlighting
|
||
|
||
The forbidden parent class reference.
|
||
|
||
[source,text]
|
||
----
|
||
class Foo(BaseException)
|
||
^^^^^^^^^^^^^
|
||
----
|
||
|
||
endif::env-github,rspecator-view[]
|