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PEP 749: Use __format__ instead of .format as param name #3993

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PEP 749: Use __format__ instead of .format as param name #3993

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PEP 749: Use __format__ instead of .format as param name
JelleZijlstra Sep 24, 2024
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Update peps/pep-0749.rst
JelleZijlstra Sep 26, 2024
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14 changes: 8 additions & 6 deletions peps/pep-0749.rst
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Expand Up @@ -710,12 +710,14 @@ Signature of ``__annotate__`` functions

However, using ``format`` as a parameter name could lead to collisions
if an annotation uses a class named ``format``. The parameter should be
positional-only and have a name that cannot be a legal identifier in order
to avoid this problem.

The current implementation uses the name ``.format`` with a leading
dot, but the exact name should be considered an implementation detail
and cannot be relied upon.
positional-only and have a name that does not coincide with an
identifier used by user code. We propose to use the name ``__format__``,
as names with double underscores are reserved for the Python implementation.

A previous version of this PEP proposed using the name ``.format`` with a
leading dot. While ``.format`` has the advantage that it cannot collide with any
identifier, reserved or not, it also prevents ``inspect.signature``
from creating a signature for annotate functions.

The documentation may still use the name ``format`` for simplicity.

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