Local type inference of numeric variables

I have a very simple example program that produces surprising and (I think...) wrong behavior:

foo = 0

foo = 1.0

Running mypy against this file yields

test.py:3: error: Incompatible types in assignment (expression has type "float", variable has type "int")

But foo could(/should) be inferred as a float in this environment. I draw this conclusion from PEP-484

when an argument is annotated as having type float, an argument of type int is acceptable

(although this is not about function arguments per se).

I know that some improvements have been recently been made to type inference in 0.770 to use information from second (or subsequent) assignments, rather than just the first assignment. So maybe a widening from int to float could be implemented in the same way...?

Reproduisez le comportement avec l’exemple test.py à l’aide de mypy, puis examinez les modifications locales d’inférence de types référencées pour la version 0.770 ainsi que les recommandations pertinentes de PEP-484. La tâche sera terminée lorsqu’il aura été établi si une variable à laquelle un int est affecté peut ensuite être élargie en float et que le comportement d’affectation qui en résulte sera couvert par des tests.