def libsolv_formatted_evr(epoch, version, release):
    """Create an epoch-version-release string from the separate values.

    Pulp stores epoch-version-release separately, libsolv uses them together.
    Convert from Pulp separate values to a combined EVR formatted as libsolv expects.
    """
    if version is None:
        return None
    return '{}{}{}'.format('{}:'.format(epoch) if epoch else '', version, 
        '-{}'.format(release) if release else '')
