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[mypyc] Fix evaluation order of multiple assignment from an iterable - #22329
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Fixes mypyc/mypyc#793. When unpacking an arbitrary iterable in a multiple assignment, mypyc interleaved getting items from the iterator and assigning them to the lvalues, and with a starred lvalue the items after the star were assigned in reverse order: ```python o.x, o.y = it # Was: o.x = next(it); o.y = next(it) ``` Python first gets all the items (and checks that the number of items is correct) before performing any assignments. Now mypyc does the same, and the lvalues are always assigned from left to right. This was already the case for lists and tuples.
p-sawicki
approved these changes
Oct 30, 2026
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Fixes mypyc/mypyc#793.
Closes #10444 (this fixes an additional use case and has run tests).
When unpacking an arbitrary iterable in a multiple assignment, mypyc
interleaved getting items from the iterator and assigning them to the
lvalues, and with a starred lvalue the items after the star were
assigned in reverse order:
Python first gets all the items (and checks that the number of items
is correct) before performing any assignments. Now mypyc does the same,
and the lvalues are always assigned from left to right. This was
already the case for lists and tuples.