input: Write a function to print the maximum number from a given list of integers. If the list is empty, the function should print "No numbers in the list". The function should return the maximum number or the message "No numbers in the list" if the list is empty.
  assert max_num([5, 4, 2, 7, 12]) == 12
  assert max_num([-1, -5, -10, -2]) == -1
  assert max_num([]) == "No numbers in the list"
  assert max_num([3]) == 3
output: def max_num(lst):
      if not lst:
          return "No numbers in the list"
      return max(lst)