input: Write a Python function to execute a valid insertion sort on a given list of integers. The function should return the sorted list.
  
  
  def insertion_sort(arr):
      for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j = j - 1
          arr[j + 1] = key
      return arr
  
  
  assert insertion_sort([5, 2, 4, 6, 1, 3]) == [1, 2, 3, 4, 5, 6]
  assert insertion_sort([31, 41, 59, 26, 41, 58]) == [26, 31, 41, 41, 58, 59]
  assert insertion_sort([0, 0, 0, 0]) == [0, 0, 0, 0]
  assert insertion_sort([]) == []
  assert insertion_sort([1]) == [1]
output: def insertion_sort(arr):
      for i in range(1, len(arr)):
          key = arr[i]
          j = i - 1
          while j >= 0 and key < arr[j]:
              arr[j + 1] = arr[j]
              j = j - 1
          arr[j + 1] = key
      return arr