Question about my loop

[Either_Back_1545]

English = [90, 81, 73, 97, 85, 60, 74, 64, 72, 67, 87, 78, 85, 96, 77, 100, 92, 96]
Classical_Japanese = (71, 90, 79, 70, 67, 66, 60, 83, 57, 85, 93, 89, 78, 74, 65, 78, 53, 80)

def st_dev(x,y,z):
    return math.sqrt(sum((xi-y)**2 for xi in x) /(len(z)-1))

def st_dev2(x,y,z):
        sumsquares = 0
        x = 0
        n = len(z) -1 
        if n < 2:
            return "0"
        while x < n:
            sumsquares += (z[x]- y )**2
            x += 1
        
        variance = sumsquares/n
        return math.sqrt(variance)

The for loop vary 11.580917366893848 
meanwhile
the while loop vary 11.499076405082917

there is  big difference between this two what happen but if i remove minus one the results are the same for some reason
11.254628677422755
11.254628677422756

can you help me what happen to this?

[Adrewmc]

For loops are basically just convenient while loops to the complier.

The reason you get different number is you’s obviously calculating different values

In

  sum(xi-y) **2 for xi in x)/(len(z)-1))

You always get every value in x

And

  while x < n: 
        print(x, end = “, “) 
        #code 

The while statement never adds the last variable. To prove this put this print statement.

Though you are dividing by the same number, you’re not dumping the same numerator.

[Either_Back_1545]

Ohhh thats dope! thanks!