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Add warning about generators for parametrizing class or module #13742

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Update parametrize.rst
andrewwillowen Sep 21, 2025
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[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Sep 21, 2025
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9 changes: 9 additions & 0 deletions doc/en/how-to/parametrize.rst
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Expand Up @@ -194,6 +194,15 @@ To get all combinations of multiple parametrized arguments you can stack
This will run the test with the arguments set to ``x=0/y=2``, ``x=1/y=2``,
``x=0/y=3``, and ``x=1/y=3`` exhausting parameters in the order of the decorators.

.. warning::

Do not use a generator as the value argument for
:ref:`pytest.mark.parametrize ref` when decorating a class or module:
the first test will consume the values of the generator and
subsequent tests will be skipped because the generator is empty.

Use a list or other iterable instead of a generator.

.. _`pytest_generate_tests`:

Basic ``pytest_generate_tests`` example
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