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.
80 lines
2.5 KiB
Plaintext
80 lines
2.5 KiB
Plaintext
== Why is this an issue?
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In Python 3, attempting to catch in an ``++except++`` statement an object which does not derive from BaseException will raise a ``++TypeError++``. In Python 2 it is possible to raise old-style classes but this shouldn't be done anymore in order to be compatible with Python 3.
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In order to catch multiple exceptions in an ``++except++`` statement, a tuple of exception classes should be provided.
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If you are about to create a custom Exception class, note that custom exceptions should inherit from ``++Exception++``, not ``++BaseException++``. ``++Exception++`` allows people to catch all exceptions except the ones explicitly asking the interpreter to stop, such as ``++KeyboardInterrupt++`` and https://docs.python.org/3/library/exceptions.html#GeneratorExit[``++GeneratorExit++``] which is not an error. See https://www.python.org/dev/peps/pep-0352/#exception-hierarchy-changes[PEP 352] for more information.
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This rule raises an issue when the expression used in an ``++except++`` statement is not a class deriving from ``++BaseException++`` nor a tuple of such classes.
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=== Noncompliant code example
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[source,python]
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----
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class CustomException:
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"""An Invalid exception class."""
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try:
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"a string" * 42
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except CustomException: # Noncompliant
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print("exception")
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except (None, list()): # Noncompliant * 2
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print("exception")
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try:
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"a string" * 42
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except [TypeError, ValueError]: # Noncompliant. Lists are not accepted.
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print("exception")
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except {TypeError, ValueError}: # Noncompliant. Sets are not accepted.
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print("exception")
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----
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=== Compliant solution
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[source,python]
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----
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class MyError(Exception):
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pass
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try:
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"a string" * 42
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except (MyError, TypeError):
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print("exception")
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----
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== Resources
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* Python documentation - https://docs.python.org/3/tutorial/errors.html[Errors and Exceptions]
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* Python documentation - https://docs.python.org/3/reference/compound_stmts.html#except[the ``++try++`` statement]
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* https://www.python.org/dev/peps/pep-0352/#exception-hierarchy-changes[PEP 352 - Required Superclass for Exceptions]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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* Change this expression to be a class deriving from BaseException or a tuple of such classes.
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=== Highlighting
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The expression which does not resolve in a valid exception class or a tuple of such classes.
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'''
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== Comments And Links
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(visible only on this page)
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include::../comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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