python3.7 IndexError：列表索引超出范围问题

Question

I have faced an error IndexError: list index out of range when I ran my_function(1, data) . This function should find distance between given point id and other points.

Code:

import math 

p = []
point_dist = []
distance = 0
data = [[1, 5, 2], [2, 6, 2], [3, 7, 2], [4, 8, 2]]

def my_function(point_id,data):
    print(len(data))   
    p.append(data[point_id])
    data.pop(point_id)
    print(len(data))

    for i in range(0, 3, 1):
        for j in range(0, 3, 1):
            distance = math.sqrt(pow(p[0][j] - data[i][j], 2))

Error :

File "C:\Anaconda3\lib\site-packages\spyder_kernels\customize\spydercustomize.py", line 110, in execfile
    exec(compile(f.read(), filename, 'exec'), namespace)

File "C:/Users/ay/YandexDisk/python/1/untitled1.py", line 13, in <module>
    distance=math.sqrt(pow(p[0][j]-data[i][j],2))

IndexError: list index out of range

Answer 1

You never called your function my_function which populate you array p . So your array is empty, and you can't access the [0][j] element.

Answer 2

You only defined a function with the name my_function() Then you have to call it first to get p list . Furthermore I prefer explicitely returning p and data :

import math 

p=[]
point_dist=[]
distance=0
data=[[1,5,2],[2,6,2],[3,7,2],[4,8,2]]

def my_function(point_id, data):
    print(len(data))   
    p.append(data[point_id])
    data.pop(point_id)
    print(len(data))

    return p, data

p, data = my_function(1, data)

for i in range(0,3,1):
    for j in range(0,3,1):
     distance=math.sqrt(pow(p[0][j]-data[i][j],2))

Out:

4
3