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.
92 lines
2.3 KiB
Plaintext
92 lines
2.3 KiB
Plaintext
== Why is this an issue?
|
||
|
||
Exception chaining enables users to see if an exception was triggered by another exception (see https://www.python.org/dev/peps/pep-3134/[PEP-3134]). Exceptions are chained using either of the following syntax:
|
||
|
||
* ``++raise NewException() from chained_exception++``
|
||
* ``++new_exception.__cause__ = chained_exception++``
|
||
|
||
It is also possible to erase a chaining by setting ``++new_exception.__cause__ = None++`` or using ``++except ... from None++`` (see https://www.python.org/dev/peps/pep-0409/[PEP-409]).
|
||
|
||
|
||
Chaining will fail and raise a ``++TypeError++`` if something else than ``++None++`` or a valid exception, i.e. an instance of ``++BaseException++`` or of a subclass, is provided.
|
||
|
||
|
||
=== Noncompliant code example
|
||
|
||
[source,python]
|
||
----
|
||
class A:
|
||
pass
|
||
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
new_exc = TypeError("new")
|
||
new_exc.__cause__ = A() # Noncompliant
|
||
raise new_exc
|
||
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
raise TypeError("new") from "test" # Noncompliant
|
||
----
|
||
|
||
|
||
=== Compliant solution
|
||
|
||
[source,python]
|
||
----
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
new_exc = TypeError("new")
|
||
new_exc.__cause__ = None # Ok
|
||
raise new_exc
|
||
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
new_exc = TypeError("new")
|
||
new_exc.__cause__ = e # Ok
|
||
raise new_exc
|
||
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
raise TypeError("new") from None # Ok
|
||
|
||
try:
|
||
raise ValueError("orig")
|
||
except ValueError as e:
|
||
raise TypeError("new") from e # Ok
|
||
----
|
||
|
||
|
||
== Resources
|
||
|
||
* PEP 3134 – https://www.python.org/dev/peps/pep-3134/[Exception Chaining and Embedded Tracebacks]
|
||
* PEP 409 – https://www.python.org/dev/peps/pep-0409/[Suppressing exception context]
|
||
* 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[Built-in Exceptions]
|
||
|
||
ifdef::env-github,rspecator-view[]
|
||
|
||
'''
|
||
== Implementation Specification
|
||
(visible only on this page)
|
||
|
||
=== Message
|
||
|
||
Replace this expression of type X with an exception or None
|
||
|
||
|
||
=== Highlighting
|
||
|
||
* In a "raise X from Y" statement:
|
||
** highlight Y
|
||
* In an "myexception.__cause__ = Y" statement:
|
||
** highlight Y
|
||
|
||
|
||
endif::env-github,rspecator-view[]
|