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Modernize raise-not-implemented

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Joe Farebrother
2025-07-17 10:02:00 +01:00
parent 2ed54d52ad
commit 680e31dc48
3 changed files with 25 additions and 13 deletions
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19
python/ql/src/Exceptions/NotImplementedIsNotAnException.qhelp
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@@ -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>
@@ -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>