Every Operator Is a Method: Meet Python's Dunder Names

Why does `return 1/self` fail on a fraction object, and what hidden method is `*` actually running every time you use it?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

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Exercise 1 of 5

A method that hands the answer back

The SimpleFraction class below stores two integers and has one unfinished method. Fill in the body of get_inverse so that it returns a float representing 1 divided by the fraction itself, then build the fraction three over four and assign the object to frac.

Careful: 1/self is not something Python knows how to compute. Only the two integers inside the object are things it can divide.

class SimpleFraction(object):
    """ A number represented as a fraction """

    def __init__(self, num, denom):
        """ num and denom are integers """
        self.num = num
        self.denom = denom

    def get_inverse(self):
        """ Returns a float representing 1/self """
        ...  # your code here


# The fraction 3 over 4, as an object.
frac = ...  # your code here

class SimpleFraction(object):
    """ A number represented as a fraction """

    def __init__(self, num, denom):
        """ num and denom are integers """
        self.num = num
        self.denom = denom

    def get_inverse(self):
        """ Returns a float representing 1/self """
        ...  # your code here


# The fraction 3 over 4, as an object.
frac = ...  # your code here

Python runs in your browser

⌘/Ctrl + Enter runs

`frac` is the fraction the prompt asks for

`get_inverse` hands back a float

flips any fraction the right way up

leaves the fraction it was called on untouched

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