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

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

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

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]

It seems this is fixed since version 1.16

Confirmed this is fixed

Navigation Menu

Repository navigation

Unexpected "incompatible type" error when chaining bytes(filter()) #12247

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Unexpected "incompatible type" error when chaining bytes(filter()) #12247

Description

Activity

ion201 commented on Feb 23, 2022

armoha commented on Dec 31, 2022

randolf-scholz commented on Nov 4, 2026

ion201 commented on Nov 4, 2026

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions