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Python: Modernise raise-not-implemented query #20086

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Python: Modernise raise-not-implemented query #20086

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680e31d
Modernize raise-not-implemented
joefarebrother Jul 17, 2025
57f1d07
Undo module deprecation (used by another quality query)
joefarebrother Jul 17, 2025
f2dd96e
Update python/ql/src/Exceptions/NotImplementedIsNotAnException.qhelp
joefarebrother Jul 17, 2025
6d33a7e
Update test output
joefarebrother Jul 17, 2025
8ccb2ed
Merge remote-tracking branch 'origin/python-qual-raise-not-implemente…
joefarebrother Jul 18, 2025
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19 changes: 10 additions & 9 deletions python/ql/src/Exceptions/NotImplementedIsNotAnException.qhelp
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Expand Up @@ -4,25 +4,25 @@
<qhelp>
<overview>

<p><code>NotImplemented</code> is not an Exception, but is often mistakenly used in place of <code>NotImplementedError</code>.
Executing <code>raise NotImplemented</code> or <code>raise NotImplemented()</code> will raise a <code>TypeError</code>.
When <code>raise NotImplemented</code> is used to mark code that is genuinely never called, this mistake is benign.

However, should it be called, then a <code>TypeError</code> will be raised rather than the expected <code>NotImplemented</code>,
which might make debugging the issue difficult.
<p>
The constant <code>NotImplemented</code> is not an <code>Exception</code>, but is often confused for <code>NotImplementedError</code>.
If it is used as an exception, such as in <code>raise NotImplemented</code> or <code>raise NotImplemented("message")</code>,
a <code>TypeError</code> will be raised rather than the expected <code>NotImplemented</code>. This may make debugging more difficult.
</p>

<p>The correct use of <code>NotImplemented</code> is to implement binary operators.
<p><code>NotImplemented</code> should only be used as a special return value for implementing special methods such as <code>__lt__</code>.
Code that is not intended to be called should raise <code>NotImplementedError</code>.</p>

</overview>
<recommendation>
<p>Replace uses of <code>NotImplemented</code> with <code>NotImplementedError</code>.</p>
<p>If a <code>NotImplementedError</code> is intended to be raised, replace the use of <code>NotImplemented</code>
with that. If <code>NotImplemented</code> is intended to be returned rather than raised, replace the <code>raise</code> with <code>return NotImplemented</code>
</p>
</recommendation>
<example>

<p>
In the example below, the method <code>wrong</code> will incorrectly raise a <code>TypeError</code> when called.
In the following example, the method <code>wrong</code> will incorrectly raise a <code>TypeError</code> when called.
The method <code>right</code> will raise a <code>NotImplementedError</code>.
</p>

Expand All @@ -34,6 +34,7 @@ The method <code>right</code> will raise a <code>NotImplementedError</code>.
<references>

<li>Python Language Reference: <a href="https://docs.python.org/library/exceptions.html#NotImplementedError">The NotImplementedError exception</a>.</li>
<li>Python Language Reference: <a href="https://docs.python.org/3/library/constants.html#NotImplemented">The NotImplemented constant</a>.</li>
<li>Python Language Reference: <a href="https://docs.python.org/3/reference/datamodel.html#emulating-numeric-types">Emulating numeric types</a>.</li>

</references>
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17 changes: 13 additions & 4 deletions python/ql/src/Exceptions/NotImplementedIsNotAnException.ql
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@@ -1,6 +1,6 @@
/**
* @name NotImplemented is not an Exception
* @description Using 'NotImplemented' as an exception will result in a type error.
* @name Raising `NotImplemented`
* @description Using `NotImplemented` as an exception will result in a type error.
* @kind problem
* @problem.severity warning
* @sub-severity high
Expand All @@ -12,8 +12,17 @@
*/

import python
import Exceptions.NotImplemented
import semmle.python.ApiGraphs

predicate raiseNotImplemented(Raise raise, Expr notImpl) {
exists(API::Node n | n = API::builtin("NotImplemented") |
notImpl = n.getACall().asExpr()
or
n.asSource().flowsTo(DataFlow::exprNode(notImpl))
) and
notImpl = raise.getException()
}

from Expr notimpl
where use_of_not_implemented_in_raise(_, notimpl)
where raiseNotImplemented(_, notimpl)
select notimpl, "NotImplemented is not an Exception. Did you mean NotImplementedError?"
2 changes: 1 addition & 1 deletion python/ql/test/query-tests/Exceptions/general/NotImplementedIsNotAnException.expected
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| exceptions_test.py:170:11:170:24 | NotImplemented | NotImplemented is not an Exception. Did you mean NotImplementedError? |
| exceptions_test.py:173:11:173:24 | NotImplemented | NotImplemented is not an Exception. Did you mean NotImplementedError? |
| exceptions_test.py:173:11:173:26 | NotImplemented() | NotImplemented is not an Exception. Did you mean NotImplementedError? |