list[I] becomes a list instead of an item

Question

I am a high school student doing a simple merge sort algorithm, but I encountered below error message. Help is much appreciated!

File "main.py", line 22, in mergesort
if l_list[i] <= r_list[j]:

TypeError: ‘<=’ not supported between instances of ‘int’ and ‘list’

Here’s my code:

list = [1, 3, 5, 6, 2]

def mergesort(list):
    n = len(list)

    if n <= 1:
      return

    mid_cut = n // 2
    l_list = list[:mid_cut]
    r_list = list[mid_cut:]
    mergesort(l_list)
    mergesort(r_list)

    i = 0
    j = 0
    list.clear()

    while i < len(l_list) and j < len(r_list):
      if l_list[i] <= r_list[j]:
        list.append(l_list[i])
        i += 1
      else:
        list.append(r_list[j])
        j += 1

    if i < len(l_list):
      list.append(l_list[i:])
    else:
      list.append(r_list[j:])

mergesort(list)

I tried extracting items from two local lists and compare them, but one of the "item" turned into a list somehow.

Asked By: Aaron Yuan

||

Source

Answer 1

In this code, you append slices to list.

if i < len(l_list):
    list.append(l_list[i:])
else:
    list.append(r_list[j:])

Use list.extend(…) instead:

if i < len(l_list):
    list.extend(l_list[i:])
else:
    list.extend(r_list[j:])

Answered By: vvvvvvvvvvv

Answer 2

list is reserved word in python, name it something other than list it may be conflicting with your code.

Have a look at this.

def mergeSort(array):
        if len(array) > 1:
    
            #  r is the point where the array is divided into two subarrays
            r = len(array)//2
            L = array[:r]
            M = array[r:]
    
            # Sort the two halves
            mergeSort(L)
            mergeSort(M)
    
            i = j = k = 0
    
            # Until we reach either end of either L or M, pick larger among
            # elements L and M and place them in the correct position at A[p..r]
            while i < len(L) and j < len(M):
                if L[i] < M[j]:
                    array[k] = L[i]
                    i += 1
                else:
                    array[k] = M[j]
                    j += 1
                k += 1
    
            # When we run out of elements in either L or M,
            # pick up the remaining elements and put in A[p..r]
            while i < len(L):
                array[k] = L[i]
                i += 1
                k += 1
    
            while j < len(M):
                array[k] = M[j]
                j += 1
                k += 1
    
    
    # Print the array
    def printList(array):
        for i in range(len(array)):
            print(array[i], end=" ")
        print()
    
    
    # Driver program
    if __name__ == '__main__':
        array = [6, 5, 12, 10, 9, 1]
    
        mergeSort(array)
    
        print("Sorted array is: ")
        printList(array)

Answered By: Vishal Arpit Kumar

list[I] becomes a list instead of an item

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