why would you use %= in Python?

Question

I understand how it works, but in what situation would you use this?

Answer 1

Modulo operator is not a python-specific thing. It is widely used in mathematics, for example in calculating greatest common divisor:
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from functools import reduce

numlist = [54, 144, 18]

def gcd(num1, num2):
res = num1 % num2
if res == 0:
return num2
else:
return gcd(num2, res)

print(reduce(gcd,numlist))
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Modulo is the key tool for Fermat's Little Theorem primality test, and has lots of other uses.