Returns a list of two-tuples containing (operator, version).

def _parse_version_string(version_conditions_string):
    '''
    Returns a list of two-tuples containing (operator, version).
    '''
    result = []
    version_conditions_string = version_conditions_string.strip()
    if not version_conditions_string:
        return result
    for version_condition in version_conditions_string.split(','):
        operator_and_version = _get_comparison_spec(version_condition)
        result.append(operator_and_version)
    return result