input: Write a function to find the largest element in a list.
  assert find_largest([9, 2, 6, 10, 4]) == 10
  assert find_largest([1, 3, 5, 7, 9]) == 9
  assert find_largest([-1, -5, -3, -4, -2]) == -1
output: def find_largest(lst):
      largest = lst[0]
      for num in lst:
          if num > largest:
              largest = num
      return largest