jbonzo/dunder

Python

Dunder Methods A.K.A Magic Methods

Dunder?

Double UNDERscore

What are dunder methods?

What are methods?

A method is a function that belongs to a class

In python these are usually noted by the dot operator

    In [1]: s = "THIS IS MY ANGRY STRING"
    In [2]: # .lower() is a string method
    In [3]: s.lower()
    Out[3]: 'this is my angry string'

Dunder methods

class Dunder(object):
    def __init__(self, phrase):
        self.phrase = phrase

    def __str__(self):
        return "This Dunder's phrase is {phrase}".format(phrase=self.phrase)

    def __len__(self):
        return len(self.phrase)

    def __add__(self, other):
        return Dunder(self.phrase + other.phrase)

Special methods that aren't explicitly called by the progammer

In [1]: from classes import Dunder

In [2]: myDunder = Dunder("Magic")

In [3]: myDunder.phrase

Out[3]: 'Magic'

In [4]: print(myDunder)
"This Dunder's phrase is Magic"

Usually are related to properties or the state of an object

In [5]: len(myDunder)
Out[5]: 5

Can also dictate the manipulation of an object

In [6]: combinedDunder = myDunder + Dunder("Methods")

In [7]: print(combinedDunder)
"This Dunder's phrase is MagicMethods"

References