Inconsistent behavior with list(reduce(...))
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bug
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Description
from functools import reduce
tmp = reduce(lambda x, y: x + y, [[1], [2]])
# this works fine
result = list(tmp)
# but this one produces an error:
# Unsupported left operand type for + ("Iterable[int]")
result = list(reduce(lambda x, y: x + y, [[1], [2]]))
$ mypy --version
mypy 0.770
Python version:
>>> sys.version
'3.8.2 (default, May 20 2020, 18:13:32) \n[GCC 7.5.0]'
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Research direction
Start by reproducing the two reduce/list snippets with the reported mypy 0.770 environment, then trace how their inferred types differ. Done means the equivalent forms receive consistent, correct type-checking behavior; no source file or test is identified in the issue.
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Assessment
- Tech stack
- python
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100