How to Mock setuptools_scm get_version in Python

This code demonstrates how to mock setuptools_scm.get_version in Python using unittest.mock.patch to test version retrieval logic without installing or relying on the actual package.

Easy Python 3.9+ Aug 9, 2026 Modern tooling 14 views 0 copies

setuptools-scm mock unittest versioning testing

Python code

16 lines
Python 3.9+
Run it 
```python
from unittest.mock import patch

def get_version_from_scm():
    try:
        import setuptools_scm
        return setuptools_scm.get_version()
    except (ImportError, LookupError):
        return None

if __name__ == "__main__":
    with patch("setuptools_scm.get_version", return_value="1.2.3"):
        print(get_version_from_scm())

    with patch("importlib.import_module", side_effect=ImportError("no setuptools_scm")):
        print(get_version_from_scm())

Output

stdout 
1.2.3
None

How it works

The patch context manager replaces the target attribute with a mock object for the duration of the with block. In the first case, setuptools_scm.get_version is mocked to return a fixed version string, so get_version_from_scm returns "1.2.3". In the second case, patching importlib.import_module with a side effect that raises ImportError simulates the absence of the setuptools_scm package, causing the function to catch the exception and return None. This pattern isolates code from external dependencies during testing, ensuring reliable unit tests.

Common mistakes

  • Patching the function after importing the module instead of patching the target reference.
  • Forgetting to include the `side_effect` argument to simulate an exception, leading to unexpected behavior.
  • Mocking `setuptools_scm.get_version` but not accounting for the `LookupError` path when the package is present but fails to determine a version.

Variations

  1. Use `pytest-mock`'s `mocker.patch` for a simpler API in pytest tests.
  2. Patch the module-level name `sys.modules` to prevent import entirely instead of mocking `import_module`.

Real-world use cases

  • Unit testing a command-line tool that retrieves its version via setuptools_scm, ensuring it works without a real repository.
  • Validating fallback logic in a package installer that handles missing version metadata gracefully.
  • Simulating an environment where setuptools_scm is not installed to test error handling in a CI pipeline.

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