# -*- coding: utf-8 -*-
# the files show how to override the operators in python
# example taken from http://blog.teamtreehouse.com/operator-overloading-python
# but there are/were some mistakes in the original
# the smartest/most complete implementation can be found in adding.py for __add__
# for more see: https://docs.python.org/2/reference/datamodel.html#special-method-names
from reverse_adding import BookRAdd as Book_r
from adding import BookAdd as Book_a
from comparison import BookCompare as Book_comp
print "reverse adding"
book1 = Book_r('a', 300)
book2 = Book_r('b', 400)
book3 = Book_r('c', 500)
summe = sum([book1, book2, book3])
print summe
print "adding"
book4 = Book_a('a', 200)
book5 = Book_a('b', 300)
print book4 + book5 # addings books
print book4 + 4 # addings books to int
print "comparisons"
book6 = Book_comp('a', 30)
book7 = Book_comp('b', 31)
print "lt: ", book6 < book7
print "le: ", book6 <= book7
print "eq: ", book6 == book7
print "ne: ", book6 != book7
print "ge: ", book6 >= book7
print "gt: ", book6 > book7
# -*- coding: utf-8 -*-
# python reverse adding
# Basically, remember how 2 + 5 and 5 + 2 are the same thing due to the commutative
# property of addition? Python takes advantage of that and swaps the operators.
# So instead of 0 + Book, it tries Book + 0. 0 + Book won’t work because the int
# class has no idea how to add itself to books. Our Book class can’t do the
# reverse add yet but we can give it the ability to.
# e.g. sum() uses reverse adding
from book import Book
class BookRAdd(Book):
def __radd__(self, other):
return self.pages + other
# -*- coding: utf-8 -*-
# adding objects in python
# overload the plus operator for a class
from book import Book
class BookAdd(Book):
def __add__(self, other):
# you can implement different behavior for different types and objects
if isinstance(other, Book):
return self.pages + other.pages
elif isinstance(other, (int, float)):
return self.pages + other
else:
return NotImplemented
# if you only want to add objects of the same type
# return self.pages + other.pages
# -*- coding: utf-8 -*-
# to make use of the comparison operators for classes
# you have to override certain methods
# __lt__() -> less than
# __le__() -> less than or equal
# __eq__() -> equals
# __ne__() -> not equals
# __ge__() -> greater than or equals
# __gt__() -> greater than
# you can implement certain comparisons for different types and classes
# but you have to know with what you compare your object value
# example implementation in adding.py for __add__()
from book import Book
class BookCompare(Book):
def __lt__(self, other):
return self.pages < other.pages
def __le__(self, other):
return self.pages <= other.pages
def __eq__(self, other):
return self.pages == other.pages
def __ne__(self, other):
return self.pages != other.pages
def __ge__(self, other):
return self.pages >= other.pages
def __gt__(self, other):
return self.pages > other.pages
# -*- coding: utf-8 -*-
# the base-class for the examples
class Book:
title = ''
pages = 0
def __init__(self, title='', pages=0):
self.title = title
self.pages = pages
def __str__(self):
return self.title
