problem with arrays and operations result beign asaigned to values

Question

Here is the python code :

x=[2, 3, 5, 7]
for i in range(1, 5000):
    if i%2:
        if i%3:
            if i%5:
                if i%7:
                    x.append(i)
x.remove(1)
a = 6
b = 2
for i in range(0, 10):
    a = x[a - b]
    b = x[a] - x[b]

I get an IndexError: list index out of range for some reason, even though x[] is 1360 and a is just 6 while b is 2 so I dont know why it is happening. Any help would be nice. I am using the python shell. Would that be a problem?

Answer 1

The problem of your code is your logic in the for loop.

You see:-

a = 6
b = 2
    for i in range(0, 10):
        a = x[a - b]
        b = x[a] - x[b]

Yes a was 6 & b was 2, but then when you enter your for loop for the first time, a's value is

x[a-b] which is x[6-2]

i.e. x[4] which gives you 11

so a's value is 11, likewise for b,

b = x[a] - x[b] # which translates to x[11] - x[2]

which becomes b=32 & the loop goes on jumping/changing the values of a & b which leads you to IndexError: list index out of range which is expected.

Try executing your program in pycharm & debug it, you would understand it better, or maybe just put some print statements.

I could not type so much in a comment, hence posted it as an answer.