input: Write a function to find the largest element in a list.
  assert find_largest_element([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]) == 9
  assert find_largest_element([-7, -5, -3, -1, -4, -2, -6]) == -1
  assert find_largest_element([1, 2, 3, 4, 5]) == 5
output: def find_largest_element(lst):
      if not lst:
          return None
      largest = lst[0]
      for num in lst[1:]:
          if num > largest:
              largest = num
      return largest