Example of validating an object in Python

type_validation.py

def validate_object(x):
    """This function validates an object x that is supposed to represent an object inside an image, and throws an exception on failure. Specifically it is checking that:
      x['polygon'] is a list of >= 3 integer (x,y) pairs representing the corners of the polygon in clockwise or anticlockwise order.
    """
    if type(x) != dict:
        raise ValueError('dict type input required.')

    if 'polygon' not in x:
        raise ValueError('polygon object required.')

    if not isinstance(x['polygon'], (list,)):
        raise ValueError('list type polygon object required.')

    points_list = x['polygon']
    if len(points_list) < 3:
        raise ValueError('More than two points required.')

    for x, y in points_list:
        if type(x) != int or type(y) != int:
            raise ValueError('integer (x,y) pairs required.')

    return