def get_path_param_names(params, deref):
    """Fetch all the names of the path parameters of an operation.

    :param params: list of all the params
    :param deref: callable that dereferences $refs

    :returns: list of the name of the path params
    """
    return [
        deref(param)['name']
        for param in params
        if deref(param)['in'] == 'path'
    ]