Python for loop: IndexError: list index out of range

I am new with Python, This is my code:

import numpy as np x = [0, 0, 0, 0, 5, 0, 10, 5] y = [4, 4, 4, 4, 9, 4, 2, 9] def unitvector1 (x,y): looplim=(len(x)+1) for i in range (0,looplim): z=i+1 alfa = np.arccos((x[i]*x[z])+(y[i]*y[z])) / ((np.sqrt(x[i] ^ 2+y[i] ^ 2) * np.sqrt(x[z] ^ 2+y[z] ^ 2))) beta =+ (180-alfa) return (beta) temp=unitvector1(x,y) print(temp) 

And I am getting this error:

IndexError: list index out of range

I tried to do it with two for loops but it did not work.

Your help is much needed, Many thanks in advance for your help.

4 Answers

Lists are indexed starting from 0, so for a list of length, say, 13, the last valid index is 12, i.e., 1 less than the length.

When you do looplim=(len(x)+1) and then for i in range (0,looplim), the last value of i is looplim-1 which is equal to len(x), so it's the length rather than 1 less than that.

looplim=len(x) for i in range(looplim-1): alfa = np.arccos((x[i]*x[z])+(y[i]*y[z])) / ((np.sqrt(x[i] ^ 2+y[i] ^ 2) * np.sqrt(x[z] ^ 2+y[z] ^ 2))) 

for each iteration value of "alfa" is nan

remove + 1 from looplim=(len(x)+1) and z = i+1 then run the code !

Okay, first u should look at your variable z. When i=7 z=8 and there are no eight’s index element in x array. Second, idk why you try “looplim”. If you want to do operations with n and n+1 elements in this way we can add next:

 def unitvector1 (x,y): for i in range (len(x)-1): z=i+1 if z==len(x)+1: z=0 alfa = np.arccos((x[i]*x[z])+(y[i]*y[z])) / ((np.sqrt(x[i] ^ 2+y[i] ^ 2) * np.sqrt(x[z] ^ 2+y[z] ^ 2))) beta =+ (180-alfa) return (beta) 

But it’s not working! Because arccos(alpha) should have alpha<|1|

If you can explain what do you want to count, maybe we can help you