List index out of range, but cannot find what is making it out of range-CodePudding

My Python code is throwing an exception here on this line, giving a "list index out of range" error, but I cannot find which part of my code is making i or r out of the array's range.

import time
import random
import math

sudoLine = [0,0,0]
possibleNums = [1,2,3]

print(len(possibleNums))

length = len(possibleNums) - 1
for i in range(3):
    r = random.randint(0,length)
    sudoLine[i] = possibleNums[r]
    possibleNums.pop(r)

print(sudoLine)

The error message is as follows:

  Message=list index out of range
  Source=C:\Users\heyma\source\repos\Sudoku Solver\Sudoku Solver\Sudoku_Solver.py
  StackTrace:
  File "C:\Users\heyma\source\repos\Sudoku Solver\Sudoku Solver\Sudoku_Solver.py", line 18, in <module> (Current frame)
    sudoLine[i] = possibleNums[r]

Sorry if this is a bad question, I'm fairly new as this is my first project!

CodePudding user response：

The issue is that the length of possibleNums is decreasing with every iteration of the for-loop but you only calculate the length variable once (before the loop). Move the line length = len(possibleNums) - 1 inside the for-loop:

import time
import random
import math

sudoLine = [0,0,0]
possibleNums = [1,2,3]

print(len(possibleNums))


for i in range(3):
    length = len(possibleNums) - 1
    r = random.randint(0,length)
    sudoLine[i] = possibleNums[r]
    possibleNums.pop(r)

print(sudoLine)

CodePudding user response：

The pop method removes an element from a list. So your possibleNums list is getting shorter with each iteration.

So at some point the value of r might be chosen to be greater that the current length of possibleNums.

CodePudding user response：

This error is thrown because the length of the possibleNums list changed after pop command was issued. Therefore reducing the number of indexes.

import random

sudoLine = [0,0,0]
possible_nums = [1,2,3]
i = 0

while len(possible_nums) > 0:
  length = len(possible_nums) - 1
  r = random.randint(0, length)
  sudoLine[i] = possible_nums[r]
  possible_nums.pop(r)
  i  = 1


print(sudoLine)