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...?

Riproduci il comportamento con l'esempio test.py usando mypy, quindi esamina le modifiche locali all'inferenza dei tipi indicate per la versione 0.770 e le indicazioni pertinenti di PEP-484. Il lavoro sarà completato quando sarà stabilito se una variabile a cui è stato assegnato un int può successivamente essere ampliata a float e sarà inclusa la copertura del comportamento di assegnazione risultante.