Issue a warning if `distribution_name` is installed.

    In a future release, this method will be updated to raise ImportError
    rather than just send a warning.

    Args:
        distribution_name (str): The name of the obsolete distribution.

def complain(distribution_name):
    """Issue a warning if `distribution_name` is installed.

    In a future release, this method will be updated to raise ImportError
    rather than just send a warning.

    Args:
        distribution_name (str): The name of the obsolete distribution.
    """
    try:
        pkg_resources.get_distribution(distribution_name)
        warnings.warn(
            "The {pkg} distribution is now obsolete. "
            "Please `pip uninstall {pkg}`. "
            "In the future, this warning will become an ImportError.".format(
                pkg=distribution_name
            ),
            DeprecationWarning,
        )
    except pkg_resources.DistributionNotFound:
        pass