error with double tuple assignment

Not sure how to describe this with words so apologies if this has already been noted.

mypy has no problem checking a = b = 1 or a, b = 1, 2, but chokes on

c = a, b = 1, 2

with KeyError: <mypy.nodes.TupleExpr object at 0x1017950b8>. Full traceback is here.

Thanks for reporting this! This is clearly a bug in how mypy handles assignment statements.

The current workaround is to split the assignment into two or more assignment statements, for example:

c = 1, 2
a, b = c

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