Python for loop: IndexError: list index out of range

Question

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.

looplim shouldn't really be len(x) + 1 since range(0, looplim) will give you a range of 0 to len(x); but while the length of x is len(x), the indices of x is from 0 to len(x) - 1 — ewokx
– ewokx, Commented Feb 15, 2022 at 9:18

Orius · Accepted Answer · 2022-02-15 09:28:56Z

3

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.

edited Feb 15, 2022 at 9:28

answered Feb 15, 2022 at 9:18

Orius

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Comments

zeeshan12396 · Accepted Answer · 2022-02-15 09:28:10Z

1

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

answered Feb 15, 2022 at 9:28

zeeshan12396

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mohamadsajedi · Accepted Answer · 2022-02-15 09:31:08Z

1

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

answered Feb 15, 2022 at 9:31

mohamadsajedi

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2 Comments

eylon levi Over a year ago

Hi thank you for your response, If I will delete z=i+1 I would get a not-defined name. I am not completely following

mohamadsajedi Over a year ago

Hello my friend... i meant you remove + 1 from z variable definition... so your z variable is equal i . Best regards

vovakirdan · Accepted Answer · 2022-02-17 08:58:14Z

1

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

edited Feb 17, 2022 at 8:58

answered Feb 15, 2022 at 9:57

vovakirdan

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