schema.py 文件源码

def valid_format_string(valid_fields):
    """
    Ensure that the provided string can be parsed as a python format string, and contains only `valid_fields`
    :param valid_fields: set or sequence of valid field names
    """
    f = Formatter()
    valid_fields = set(valid_fields)

    def validate_string(format_string):
        fields = set(field_name for _, field_name, _, _ in f.parse(format_string) if field_name)

        if fields < valid_fields:
            return format_string
        else:
            raise Invalid('format string specifies invalid field(s): %s' % (fields - valid_fields))

    return validate_string