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Unexpected "incompatible type" error when chaining bytes(filter())

Open ion201 opened this issue 3 years ago • 2 comments

Bug Report

Mypy reports a strange type error when calling bytes(filter(...)) like below.

Write the following contents to a file and run mypy:

f = filter(lambda ch: chr(ch), b"hello")
bytes(f)

bytes(filter(lambda ch: chr(ch), b"hello"))

Mypy reports an error on line 4 but not on lines 1/2, despite the two sections being functionally identical. The expected result is that there should be no errors in this code example.

> mypy /tmp/test.py
/tmp/test.py:4: error: Argument 1 to "chr" has incompatible type "SupportsIndex"; expected "int"
Found 1 error in 1 file (checked 1 source file)

Your Environment

  • Mypy version used: mypy 0.931
  • Mypy command-line flags: none
  • Mypy configuration options from mypy.ini (and other config files): none
  • Python version used: python 3.10.2
  • Operating system and version: Arch linux and windows 10

ion201 avatar Feb 23 '22 20:02 ion201

After rolling back mypy on windows, this error first appears in v0.920

ion201 avatar Feb 23 '22 20:02 ion201

The issue still exists with mypy 0.991, Python 3.11.1 and Windows 10.

def IgnoreColor(s: bytes) -> bytes:
    bytes(filter(lambda x: not (0x01 <= x <= 0x1F or x == 0x7F), s))
error: Argument 1 to "filter" has incompatible type "Callable[[Any], bool]"; expected "Callable[[int], TypeGuard[SupportsIndex]]"  [arg-type]
error: Unsupported operand types for >= ("int" and "SupportsIndex")  [operator]
error: Unsupported operand types for <= ("int" and "SupportsIndex")  [operator]

armoha avatar Dec 31 '22 14:12 armoha