_optional.py

import distutils.version
import importlib
import types
import warnings


# Adapted from:
# https://github.com/pandas-dev/pandas/blob/master/pandas/compat/_optional.py

VERSIONS = {
    "taxcalc": "2.0.0",
}


def _get_version(module: types.ModuleType) -> str:
    version = getattr(module, "__version__", None)
    if version is None:
        # xlrd uses a capitalized attribute name
        version = getattr(module, "__VERSION__", None)

    if version is None:
        raise ImportError(f"Can't determine version for {module.__name__}")
    return version


def import_optional_dependency(
    name: str, extra: str = "", raise_on_missing: bool = True,
        on_version: str = "raise"
):
    """
    Import an optional dependency.
    By default, if a dependency is missing an ImportError with a nice
    message will be raised. If a dependency is present, but too old,
    we raise.
    Parameters
    ----------
    name : str
        The module name. This should be top-level only, so that the
        version may be checked.
    extra : str
        Additional text to include in the ImportError message.
    raise_on_missing : bool, default True
        Whether to raise if the optional dependency is not found.
        When False and the module is not present, None is returned.
    on_version : str {'raise', 'warn'}
        What to do when a dependency's version is too old.
        * raise : Raise an ImportError
        * warn : Warn that the version is too old. Returns None
        * ignore: Return the module, even if the version is too old.
          It's expected that users validate the version locally when
          using ``on_version="ignore"`` (see. ``io/html.py``)
    Returns
    -------
    maybe_module : Optional[ModuleType]
        The imported module, when found and the version is correct.
        None is returned when the package is not found and `raise_on_missing`
        is False, or when the package's version is too old and `on_version`
        is ``'warn'``.
    """
    msg = (
        f"Missing optional dependency '{name}'. {extra} "
        f"Use pip or conda to install {name}."
    )
    try:
        module = importlib.import_module(name)
    except ImportError:
        if raise_on_missing:
            raise ImportError(msg) from None
        else:
            return None

    minimum_version = VERSIONS.get(name)
    if minimum_version:
        version = _get_version(module)
        if distutils.version.LooseVersion(version) < minimum_version:
            assert on_version in {"warn", "raise", "ignore"}
            msg = (
                f"microdf requires version '{minimum_version}' or newer of "
                f"'{name}' "
                f"(version '{version}' currently installed)."
            )
            if on_version == "warn":
                warnings.warn(msg, UserWarning)
                return None
            elif on_version == "raise":
                raise ImportError(msg)

    return module