How do you find the index of an element in an Array on Python while in loop

i is an index and you are updating it too often. Move the indentation of i = i+1 to get rid of the index out of bounds.

while i<size(Array):
      for index, k in enumerate(Array1):
             if (k==Array[i]):
                   print index
      i=i+1

If you only want the first index (or there will only be one index) then you can use the index function:

for i in array2:
    if i in array1:
        print array1.index(i)

To get a list of the indices:

print [array2.index(i) for i in array1 if i in array2]

You can test whether a value is in a list by using the in membership testing operator:

Array = [1,2,3,4,5,6,7,8]
Array1 = [2,9,3,9,1,9,2]

for i, value in enumerate(Array1):
    if value in Array:
        print i

output

0
2
4
6

It looks as if you want to print all indexes in the inner array where the value matches a value in the output array:

array1 = [1,2,3,4,5,6,7,8]
array2 = [2,9,3,9,1,9,2]
for i,a1 in enumerate(array1):
    for j,a2 in enumerate(array2):
        if a1 == a2:
            print j

Output:

4
0
6
2

If you want to collect the indices, you a list comprehension:

print [j for i,a1 in enumerate(array1) for j,a2 in enumerate(array2) if a1 == a2]

Output:

[4, 0, 6, 2]

Or maybe in sorted order:

print sorted(j for i,a1 in enumerate(array1) for j,a2 in enumerate(array2) if a1 == a2)

Output:

[0, 2, 4, 6]

while i<size(Array):
      for index, k in enumerate(Array1):
             if (k==Array[i]):
                   print index
                   i=i+1

If I understand correctly, you are thinking that i shouldn't go above the size of Array, because you have a while i < size(Array) But the while condition only controls whether the loop will repeat, it does not guarantee that i will remain less then size throughout the loop.

You seem to be thinking that this will loop over the arrays once, but because one loop is inside the other: the loop itself will be repeated.

In this case, i is incremented inside the inner loop once for every element in Array1, which causes it to become too high for indexing Array.

I think what you want is to iterate over both lists at the same time. Don't do this by creating two loops, you only want one loop.

for index, k in enumerate(Array):
     if k == Array1[index]:
          print index

A better approach, but perhaps harder to understand for a beginner is this:

for index, (value1, value2) in enumerate(zip(Array, Array1)):
   if value1 == value2:
        print index

Zip "zips" the two lists together which makes it really easy to iterate over both in parallel.