__setitem__ implementation in Python for Point(x,y) class

Question

I\'m trying to make a Point class in python. I already have some of the functions, like __ str__ , or __ getitem__ implemented, and it works great. The only problem I\'m fac

Answer 1

This works in python 2.6 i guess it works for 2.7 as well

The __setitem__ method accept 3 arguments (self, index, value)

in this case we want to use index as int for retrive the name of the coordinate from __slots__ tuple (check the documentation of __slots__ is really usefull for performance)

remember with __slots__ only x and y attributes are allowed! so:

p = Point()
p.x = 2
print(p.x)  # 2.0

p.z = 4  # AttributeError
print(p.z)  # AttributeError

This way is faster respect using @property decorator (when you start to have 10000+ instances)

class Point(object):
    @property
    def x(self):
        return self._data[0]  # where self._data = [x, y]
...

so this is my tip for you :)

class Point(object):

    __slots__ = ('x', 'y')  # Coordinates

    def __init__(self, x=0, y=0):
        '''
        You can use the constructor in many ways:
        Point() - void arguments
        Point(0, 1) - passing two arguments
        Point(x=0, y=1) - passing keywords arguments
        Point(**{'x': 0, 'y': 1}) - unpacking a dictionary
        Point(*[0, 1]) - unpacking a list or a tuple (or a generic iterable)
        Point(*Point(0, 1)) - copy constructor (unpack the point itself)
        '''
        self.x = x
        self.y = y

    def __setattr__(self, attr, value):
        object.__setattr__(self, attr, float(value))

    def __getitem__(self, index):
            '''
            p = Point()
            p[0]  # is the same as self.x
            p[1]  # is the same as self.y
            '''
        return self.__getattribute__(self.__slots__[index])

    def __setitem__(self, index, value):
            '''
            p = Point()
            p[0] = 1
            p[1] = -1
            print(repr(p))  # <Point (1.000000, -1.000000)>
            '''
        self.__setattr__(self.__slots__[index], value)  # converted to float automatically by __setattr__

    def __len__(self):
        '''
        p = Point()
        print(len(p))  # 2
        '''
        return 2

    def __iter__(self):
        '''
        allow you to iterate
        p = Point()
        for coord in p:
            print(coord)

        for i in range(len(p)):
            print(p[i])
        '''
        return iter([self.x, self.y])

    def __str__(self):
        return "(%f, %f)" % (self.x, self.y)

    def __repr__(self):
        return "<Point %s>" % self