#!/usr/bin/env python

# Written by: DGC

# python imports

import math

#==============================================================================

class DataCache(object):

def __init__(self):

""" A class representing cachable data, starts invalid."""

self.data = None

def __call__(self):

"""

When an instance is called it returns the stored data or None if no

data has been cached.

e.g

data = cached_data()

"""

return self.data

def __nonzero__(self):

"""

Called on bool(instance) or if(instance) returns if there is data

cached.

e.g

if (not data):

# set data

"""

return self.data is not None

def set(self, data):

""" Sets the data. """

self.data = data

def reset(self):

""" Returns the class to an invalid state. """

self.data = None

#==============================================================================

class Line(object):

def __init__(self, start, end):

"""

This is a class representing a 2D line.

Takes a start point and end point represented by two pairs.

"""

self.start = start

self.end = end

self.length_data = DataCache()

def length(self):

if (not self.length_data):

x_length = self.start[0] - self.end[0]

y_length = self.start[1] - self.end[1]

length = math.sqrt((x_length ** 2) + (y_length ** 2))

self.length_data.set(length)

else:

print("Cached value used")

return self.length_data()

#==============================================================================

if (__name__ == "__main__"):

l = Line((0, 0), (1, 0))

print(l.length())

print(l.length())