Question

There is an exercise in 6.00x edX whose answer’s suggestion provided by them is as follows:

def genPrimes():
    primes = []   # primes generated so far
    last = 1      # last number tried
    while True:
        last += 1
        for p in primes:
            if last % p == 0:
                break
        else:
            primes.append(last)
            yield last

Looking to the identation I can clearly see that this ELSE is not related to the IF. I thought it was a bug but when I executed, the code was fine and I can’t understand what is happening, what does that ELSE does?

Answer 1

else part of your for loop executes, when your for loop runs successfully without breaking in the middle of the iteration.

So, in your example, : –

if last % p == 0:
      break

if your above if condition in for loop becomes true in some iteration, it will break out of your for loop, and in that case your else will not execute.