<nothing> object is not iterable

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
compilers

Research direction

Start by reproducing the example from nothingiterable.py and compare the diagnostic for the empty-list dictionary comprehension with the described vals or [] case. Trace how mypy infers the comprehension's element types and define done as handling an empty list literal without reporting the spurious ' object is not iterable' error.

Written by the indexing model from the issue text.

Description

bug

This code:

d = {k: v for k, v in []}

gives

nothingiterable.py:1: error: '<nothing>' object is not iterable

(The real code this was derived from had vals or [], not just [], and mypy had concluded that vals was of type None, for unrelated bogus reasons).

I realize mypy doesn't know the type of list elements for an empty list, but it seems like in the case of an empty list literal it would be possible to realize that it doesn't matter, and the resulting type of d could be an uninhabited dictionary?

Dominant language
Python
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