Python Operator Overload

python-operator-overload.py

#!/usr/bin/env python

""" A simple example of overloading the plus operator.

    Instances are created by passing a notation consisting of a numerical value followed by one of the supported
    dimensions (m, cm, mm) separated by a single space.

    Adding two values initialized with different dimensions returns an object with the dimension of the first value.

    Example:
    l1 = Length('1 mm')
    l2 = Length('1 m')

    print(l1 + l2)
    # 1001.0 mm

    print(l2 + l1)
    # 1.001 m
"""

__author__  = "André Tannús"
__email__   = "andre.tannus@gmail.com"
__license__ = "MIT"
__status__  = "Prototype"

class Length:
    def __init__(self, notation):
        self.supportedDimensions = {'m':1, 'cm':1e-2, 'mm':1e-3}
        parts = notation.split(' ')
        self.magnitude = float(parts[0])
        self.dimension = parts[1]
        self.notation = notation;

    def getFactor(self, fromDim, toDim):
        return self.supportedDimensions[fromDim] / self.supportedDimensions[toDim];

    def __add__(self, operand):
        newMagnitude = self.magnitude + (operand.magnitude * self.getFactor(operand.dimension, self.dimension))
        return Length(str(newMagnitude) + ' ' + self.dimension)

    def __str__(self):
        return self.notation;

l1 = Length('1 mm')
l2 = Length('1 m')

print(l1 + l2)
# 1001.0 mm

print(l2 + l1)
# 1.001 m