`NotPython` error when processing non-Python files and measuring branch coverage

[tjkuson]

Describe the bug

When running coverage run --branch --module pytest using v7.11.1 in a project that processes non-Python files (in my case, HTML templates), I get the following error.

coverage.exceptions.NotPython: Couldn't parse '/Users/tjkuson/workspace/repro/src/repro/templates/greet.html' as Python source: 'invalid syntax' at line 1`.

This does not happen when using v7.11.0, nor does it happen when I do not measure branch coverage.

To Reproduce

What version of Python are you using?

I am using 3.14, though I have managed to reproduce the error on 3.10 as well.

What version of coverage.py shows the problem? The output of coverage debug sys is helpful.

I am using v7.11.1 (managed via uv).

$ uv run coverage debug sys
-- sys -------------------------------------------------------
               coverage_version: 7.11.1
                coverage_module: /Users/tjkuson/workspace/repro/.venv/lib/python3.14/site-packages/coverage/__init__.py
                           core: -none-
                        CTracer: available from /Users/tjkuson/workspace/repro/.venv/lib/python3.14/site-packages/coverage/tracer.cpython-314-darwin.so
           plugins.file_tracers: -none-
            plugins.configurers: -none-
      plugins.context_switchers: -none-
              configs_attempted: /Users/tjkuson/workspace/repro/.coveragerc
                                 /Users/tjkuson/workspace/repro/setup.cfg
                                 /Users/tjkuson/workspace/repro/tox.ini
                                 /Users/tjkuson/workspace/repro/pyproject.toml
                   configs_read: /Users/tjkuson/workspace/repro/pyproject.toml
                    config_file: None
                config_contents: -none-
                      data_file: -none-
                         python: 3.14.0 (main, Oct  7 2025, 09:34:52) [Clang 17.0.0 (clang-1700.3.19.1)]
                       platform: macOS-26.0.1-arm64-arm-64bit-Mach-O
                 implementation: CPython
                          build: main
                                 Oct  7 2025 09:34:52
                    gil_enabled: True
                     executable: /Users/tjkuson/workspace/repro/.venv/bin/python3
                   def_encoding: utf-8
                    fs_encoding: utf-8
                            pid: 28295
                            cwd: /Users/tjkuson/workspace/repro
                           path: /Users/tjkuson/workspace/repro/.venv/bin
                                 /opt/homebrew/Cellar/python@3.14/3.14.0_1/Frameworks/Python.framework/Versions/3.14/lib/python314.zip
                                 /opt/homebrew/Cellar/python@3.14/3.14.0_1/Frameworks/Python.framework/Versions/3.14/lib/python3.14
                                 /opt/homebrew/Cellar/python@3.14/3.14.0_1/Frameworks/Python.framework/Versions/3.14/lib/python3.14/lib-dynload
                                 /Users/tjkuson/workspace/repro/.venv/lib/python3.14/site-packages
                    environment: HOME = /Users/tjkuson
                                 PYTHONSTARTUP = /Users/tjkuson/.config/python/pythonrc.py
                   command_line: /Users/tjkuson/workspace/repro/.venv/bin/coverage debug sys
                           time: 2025-11-08 00:13:45

What versions of what packages do you have installed? The output of pip freeze is helpful.

annotated-doc==0.0.3
annotated-types==0.7.0
anyio==4.11.0
certifi==2025.10.5
click==8.3.0
coverage==7.11.1
dnspython==2.8.0
email-validator==2.3.0
fastapi==0.121.0
fastapi-cli==0.0.14
fastapi-cloud-cli==0.3.1
h11==0.16.0
httpcore==1.0.9
httptools==0.7.1
httpx==0.28.1
idna==3.11
iniconfig==2.3.0
jinja2==3.1.6
markdown-it-py==4.0.0
markupsafe==3.0.3
mdurl==0.1.2
packaging==25.0
pluggy==1.6.0
pydantic==2.12.4
pydantic-core==2.41.5
pygments==2.19.2
pytest==8.4.2
python-dotenv==1.2.1
python-multipart==0.0.20
pyyaml==6.0.3
rich==14.2.0
rich-toolkit==0.15.1
rignore==0.7.6
sentry-sdk==2.43.0
shellingham==1.5.4
sniffio==1.3.1
starlette==0.49.3
typer==0.20.0
typing-extensions==4.15.0
typing-inspection==0.4.2
urllib3==2.5.0
uvicorn==0.38.0
uvloop==0.22.1
watchfiles==1.1.1
websockets==15.0.1

What code shows the problem? Give us a specific commit of a specific repo that we can check out. If you've already worked around the problem, please provide a commit before that fix.

https://github.com/tjkuson/coverage-repro

What commands should we run to reproduce the problem? Be specific. Include everything, even git clone, pip install, and so on. Explain like we're five!

$ git clone git@github.com:tjkuson/coverage-repro
$ cd coverage-repro
$ uv run coverage run --branch --module pytest

Expected behavior

There should be no error.

Additional context

[tjkuson]

I've bisected the regression to 31f91f8

[gaige]

I'm seeing the same problem with 7.1.1 (not 7.1.0) in a Django project using jinja2 also on 3.14.

[devdanzin]

Seems to be caused by the inclusion of PythonParser(filename=filename).parse_source():

coveragepy/coverage/sysmon.py

Lines 472 to 473 in 31f91f8

	parser = PythonParser(filename=filename)
	parser.parse_source()

I see two options to fix this:

• Add a parameter to parse_source which tells it whether to raise NotPython or not.
• Catch (and ignore) NotPython in get_multiline_map.

I can work on a PR once a way to fix the issue is chosen. I favor the second option, but am not sure there isn't a better one I'm not seeing.

[nedbat]

Sorry about this regression, I'll fix it today.

[tjkuson]

Sorry about this regression, I'll fix it today.

Thank you! I really appreciate the work you do here.

[eirkkr]

Just came across this bug as well, interestingly if I swap to ctrace core then I don't get the error, but I'll wait for a fix :), thanks @nedbat

[nedbat]

Fixed in commit 9f0753b. I thought about issuing a warning when NotPython is caught, but 99% of the time, the measurement will be accurate. It's only a slight chance that lines will be missed, so there's no warning.

[nedbat]

This is now released as part of coverage 7.11.2.