Fancy Syntax

---

It turns out that most of the common syntax in Python is really just “special methods” that can be defined in your class. Below is a list of common features you might define when writing your own classes.

Syntax	Method Call
x < y	x.__lt__(y)
x == y	x.__eq__(y)
x >= y	x.__ge__(y)
print(x)	print(x.__repr__())
x[i]	x.__getitem__(i)
x[i] = v	x.__setitem__(i, v)

For example, here is a toy class that implements all of these methods to prove that they get called when you use the syntax shown above.

class SomeClass:
    def __lt__(self, other):
        print('Calling __lt__')
        return False

    def __eq__(self, other):
        print('Calling __eq__')
        return False

    def __repr__(self):
        print('Calling __repr__')
        return 'SomeString'

    def __getitem__(self, i):
        print(f'Calling __getitem__ with {i}')
        return -1

    def __setitem__(self, i, v):
        print(f'Calling __setitem__ with {i} and {v}')
        return -1


x = SomeClass()
y = SomeClass()

print('Less Than')
print(x < y)
print()

print('Greater Than')
print(x > y)
print()

print('Equal')
print(x == y)
print()

print('Not equal')
print(x != y)
print()

print('Print')
print(x)
print()

print('Bracket Notation')
print(x[0])
x[14] = 4

Note

It turns out that because we implement __lt__ and __eq__ there is no need to implement any other comparison operators ( __le__ , __gt__, __ge__). This is why when we wrote x > y it can figure it out just from __lt__! For example, x > y can be implemented as y.__lt__(x) and x <= y could be implemented as x.__lt__(y) or x.__eq_(y)!

You could have chosen another operator besides __lt__, but basically if you implement any less than/greater than operator and equals, you get all of the others for free!