setuptools_requires_alternative.py

setuptools_requires_alternative.py

# © 2017 Dominik George <nik@naturalnet.de>
# Choose any OSI licence you like.
from pkg_resources import get_distribution

def requires_alternative(*alternatives):
    """ Allows specifying alternative requirements.

    This function takes arbitrarily many distribution specifications as arguments.
    It then checks for availability of each. If a distribution is found, the original
    specification for it is returned. If none of the alternatives is available,
    the first specified one is returned, causing setuptools to install it.
    """

    # Allow calling with both a list and several arguments
    if not isinstance(alternatives[0], str):
        alternatives = alternatives[0]

    # Iterate over all listed alternatives
    for alternative in alternatives:   
        # Try to find a distribution with this specification
        try:
            get_distribution(alternative)
            # If we got here, return this specification as requirement,
            # it was the first we found
            return alternative
        except:   
            # Not found, go on
            continue

    # If we got here, no alternative is installed yet, so return the first
    return alternatives[0]