What causes "Can't determine version for {module.__name__}" in pandas-dev/pandas?

Ensure the real, packaged version of the dependency is installed (pip install --force-reinstall ).

pandas-dev/pandas · error · ImportError

Can't determine version for {module.name}

Error message

Can't determine version for {module.__name__}

What it means

Raised by get_version (compat/_optional.py:76-84) when an imported module has no __version__ attribute. pandas uses this to compare dependency versions against required minimums (VERSIONS dict). If the module loaded but its package didn't expose __version__, pandas cannot verify the minimum and raises ImportError. Note: psycopg2 is special-cased (its version string is split).

Source

Thrown at pandas/compat/_optional.py:80

# these two names are different.

INSTALL_MAPPING = {
    "bs4": "beautifulsoup4",
    "bottleneck": "Bottleneck",
    "jinja2": "Jinja2",
    "lxml.etree": "lxml",
    "odf": "odfpy",
    "python_calamine": "python-calamine",
    "sqlalchemy": "SQLAlchemy",
    "tables": "pytables",
}


def get_version(module: types.ModuleType) -> str:
    version = getattr(module, "__version__", None)

    if version is None:
        raise ImportError(f"Can't determine version for {module.__name__}")
    if module.__name__ == "psycopg2":
        # psycopg2 appends " (dt dec pq3 ext lo64)" to its version
        version = version.split()[0]
    return version


@overload
def import_optional_dependency(
    name: str,
    extra: str = ...,
    min_version: str | None = ...,
    *,
    errors: Literal["raise"] = ...,
) -> types.ModuleType: ...


@overload
def import_optional_dependency(

View on GitHub (pinned to 71959b8cb9)

Solutions

Ensure the real, packaged version of the dependency is installed (pip install --force-reinstall <pkg>).
Check for a local file/module shadowing the package: import <pkg>; print(<pkg>.__file__).
If you control the dependency, add __version__ to its package __init__.
If you must use a version-less module, call import_optional_dependency with errors='ignore' (you lose version gating).

Example fix

# before — local 'tables.py' shadows pytables, no __version__
import_optional_dependency('tables', min_version='3.0')

# after
pip install --force-reinstall tables  # or rename/remove the shadowing file

Defensive patterns

Strategy: validation

Validate before calling

import importlib
mod = importlib.import_module(name)
if not hasattr(mod, '__version__'):
    raise ImportError(f'{name} has no __version__; reinstall the packaged version')

Try / catch

try:
    import_optional_dependency(name, min_version=minimum)
except ImportError:
    # module present but version-less — reinstall or pass errors='ignore'
    ...

Prevention

Install dependencies from PyPI/conda rather than vendored stubs.
Check for local same-name files shadowing the package.
Use pip show <pkg> to confirm installed package metadata is present.

When it happens

Trigger: import_optional_dependency(name, min_version=...) calls get_version on the imported module; if module.__version__ is None/missing, line 80 raises. Also reachable by calling get_version directly on a module lacking __version__.

Common situations: A lightweight/stub package that imports successfully but omits __version__ (some C-extensions, vendored forks, namespace packages); a module shadowed by a local file of the same name that lacks version metadata; an in-development checkout without packaged metadata.

Related errors

AI-assisted analysis of pandas-dev/pandas@71959b8cb9 (2026-08-07). Data as JSON: /api/errors/f49819a2366e8b3d. Report an issue: GitHub.