8.1. Operator About

  • Operator Overload

  • Operator Overload is the Pythonic way

  • Operator Overload allows readable syntax

  • Operator Overload allows simpler operations

  • All examples in this chapter uses dataclasses for you to focus on the important code, not boilerplate code just to make it works

  • https://github.com/python/cpython/blob/main/Grammar/python.gram#L695

8.1.1. Operators

8.1.2. Recap

>>> a = int(1)
>>> b = int(2)
>>> a + b
3

>>> a = float(1.0)
>>> b = float(2.0)
>>> a + b
3.0

>>> a = str('1')
>>> b = str('2')
>>> a + b
'12'

>>> a = list([1])
>>> b = list([2])
>>> a + b
[1, 2]

>>> a = tuple((1,))
>>> b = tuple((2,))
>>> a + b
(1, 2)

8.1.3. Problem

  • Class 'Vector' does not define '__add__', so the '+' operator cannot be used on its instances

  • dataclass is used to generate __init__() and __repr__()

  • dataclass does not have any influence on addition

>>> class Vector:
...     def __init__(self, x, y):
...         self.x = x
...         self.y = y
...
...     def __repr__(self):
...         return f'Vector(x={self.x}, y={self.y})'
>>>
>>>
>>> a = Vector(x=1, y=2)
>>> b = Vector(x=2, y=3)

>>> a + b
Traceback (most recent call last):
TypeError: unsupported operand type(s) for +: 'Vector' and 'Vector'

8.1.4. Solution

  • Implement __add__() method

  • Takes two arguments, self and other

  • Other is another instance of the same class

  • Returns a new instance of the same class

>>> class Vector:
...     def __init__(self, x, y):
...         self.x = x
...         self.y = y
...
...     def __repr__(self):
...         return f'Vector(x={self.x}, y={self.y})'
...
...     def __add__(self, other):
...         new_x = self.x + other.x
...         new_y = self.y + other.y
...         return Vector(x=new_x, y=new_y)
>>>
>>>
>>> a = Vector(x=1, y=2)
>>> b = Vector(x=2, y=3)

>>> a + b
Vector(x=3, y=5)

8.1.5. Further Reading