Overloading * and float() for a Fraction Class

How do `a * b`, `a.__mul__(b)` and `Fraction.__mul__(a, b)` all run the same code, and why is only the last handed `self` by hand?

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.

0 / 5 passed

The Fraction class below can build itself and print itself, but a * b currently fails — nothing in the class says what a star between two fractions should mean.

Add __mul__, the method Python runs behind the * shorthand, so that multiplying two fractions multiplies the numerators, multiplies the denominators, and hands back a new Fraction object rather than a float. Then multiply a, which is 2/5, by b, which is 3/7, and assign the result to product.
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class Fraction(object): """ A number of the form num/denom, where both are integers """ def __init__(self, num, denom): """ Sets the numerator and the denominator """ self.num = num self.denom = denom def __str__(self): """ Returns the fraction written as num/denom """ return str(self.num) + "/" + str(self.denom) # your code here: add the __mul__ method a = Fraction(2, 5) b = Fraction(3, 7) # The product of a and b. product = ... # your code here
class Fraction(object): """ A number of the form num/denom, where both are integers """ def __init__(self, num, denom): """ Sets the numerator and the denominator """ self.num = num self.denom = denom def __str__(self): """ Returns the fraction written as num/denom """ return str(self.num) + "/" + str(self.denom) # your code here: add the __mul__ method a = Fraction(2, 5) b = Fraction(3, 7) # The product of a and b. product = ... # your code here
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`Fraction` has a `__mul__` method
the product is a `Fraction`, not a float
multiplies numerators and denominators straight across
works for any pair of fractions, and reduces nothing

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class Fraction(object): """ A number of the form num/denom, where both are integers """ def __init__(self, num, denom): """ Sets the numerator and the denominator """ self.num = num self.denom = denom def __str__(self): """ Returns the fraction written as num/denom """ return str(self.num) + "/" + str(self.denom) # your code here: add the __mul__ method a = Fraction(2, 5) b = Fraction(3, 7) # The product of a and b. product = ... # your code here