def parse_config_vars(config_vars):
    """Convert string descriptions of config variable assignment into
    something that CrossEnvBuilder understands.

    :param config_vars:  An iterable of strings in the form 'FOO=BAR'
    :returns:            A dictionary of name:value pairs.
    """

    result = {}
    for val in config_vars:
        try:
            name, value = val.split('=', 1)
        except ValueError:
            raise ValueError("--config-var must be of the form FOO=BAR")

        result[name] = value
    return result