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[mypyc] Support "raise ... from ..." properly - #22148
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Fixes mypyc/mypyc#1224. The `from` clause of a `raise` statement was silently ignored in compiled code, so `__cause__` stayed `None` and `__suppress_context__` stayed `False`: ```python def f() -> None: try: raise KeyError() except KeyError as exc: raise ValueError() from exc # __cause__ is None when compiled ``` Now the cause is evaluated and set using a new `CPy_RaiseFrom` primitive, which follows the CPython implementation of `raise` (also with respect to exception classes, `from None` and invalid causes).
p-sawicki
approved these changes
Oct 9, 2026
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The
fromclause of araisestatement was silently ignored incompiled code, so
__cause__stayedNoneand__suppress_context__stayed
False.Also make error checking in raise statements a bit more compatible with CPython.
Fixes mypyc/mypyc#1224.