dict(zip()) and itertools.product

Open
#3,884 3 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Reproduce the reported error with Python 3.6.1 and mypy 0.521 using the two dict(zip()) examples in the issue. Trace how zip() and itertools.product(..., repeat=2) are typed; done means the second example is accepted without weakening the incorrect-type check, with a regression test for this case.

Written by the indexing model from the issue text.

Description

feature priority-2-low topic-plugins

I think I've noticed a tiny bug.
Python 3.6.1
mypy 0.521

from typing import Tuple, Dict
from itertools import product

# works fine
XY_1: Dict[str, Tuple[int, int]] = dict(zip('abcd', product(range(2), range(2))))
# {'a': (0, 0), 'b': (0, 1), 'c': (1, 0), 'd': (1, 1)}

# error for this one
XY_2: Dict[str, Tuple[int, int]] = dict(zip('abcd', product(range(2), repeat=2)))
# {'a': (0, 0), 'b': (0, 1), 'c': (1, 0), 'd': (1, 1)}

The dictionaries are the same.
Error output:

mypy_test.py:10: error: Argument 2 to "zip" has incompatible type Iterator[Tuple[int]]; expected Iterable[Tuple[int, int]]

I think that this is not essential. So, just in case.
Thanks for the great product!

Dominant language
Python
Stars
20.6k
Forks
3.3k
Avg merge
1d 18h
Merged PRs (30d)
54

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/mypy

All issues in python/mypy

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.