PEP-654: allow subclassing of exception groups #1872
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1st1
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Mar 16, 2021
pep-0654.rst
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| It is possible to subclass exception groups, but when doing that it is | ||
| usually necessary to specify how ``subgroup()`` and ``split()`` should | ||
| create new instances for the matching or non-matching part of the partition. | ||
| ``BaseExceptionGroup`` exposes an instance method ``derive_new(self, excs)`` |
1st1
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Mar 16, 2021
gvanrossum
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Mar 17, 2021
pep-0654.rst
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| Note that we override ``__new__`` rather than ``__init__``; this is because | ||
| ``BaseExceptionGroup`` has a ``__new__`` method whose signature doesn't match | ||
| that of our new type. Note also that our ``derive`` function does not |
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Well, it must override "the constructor" (i.e. either new or init) because it has a different signature; it must override new rather than init because ExceptionGroup has immutable fields (message and exceptions).
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Is it because of immutability, or because of the selection between ExceptionGroup and BaseExceptionGroup depending on their types? Or both?
Co-authored-by: Guido van Rossum <gvanrossum@gmail.com>
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