python / python/mypy

Failed to find exact letter case of module name when relative import on Windows OS

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bug
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Python
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Description

Bug Report

Failed to find exact letter case of module name when relative import on Windows OS.

To Reproduce

ModuleName
├─ __init__.py
├─ file.py
├─ main.py

# main.py
from .file import *

Everything is fine when the path is correct with letter case.

mypy .\ModuleName\main.py
Success: no issues found in 1 source file

But if the path of files is wrong with letter case,

mypy .\moduleName\main.py

but there will be an [import-not-found] error.

moduleName\main.py:1: error: Cannot find implementation or library stub for module named "moduleName.file"  [import-not-found]

Your Environment

  • Mypy version used: mypy 1.14.1 (compiled: yes)

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.

Research direction

Start by reproducing the Windows case-mismatch with ModuleName/init.py, file.py, and main.py, using the relative import in main.py and the two mypy commands shown. Trace how the command-line path is mapped to the module name. Done means the incorrectly cased path resolves the relative import without an import-not-found error.

Written by the indexing model from the issue text.

Assessment

Tech stack
python
Domain
compilers
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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