how to calculate distance from latitude and longitude in python?
['R = 6373.0. radius of the Earth.', 'lat1 = math. radians(52.2296756) ... ', 'lon1 = math. radians(21.0122287)', 'lat2 = math. radians(52.406374)', 'lon2 = math. radians(16.9251681)', 'dlon = lon2 - lon1. change in coordinates.', 'dlat = lat2 - lat1.', 'a = math.']