input: Write a python function to compute the sum of all positive numbers in a given list utilizing a lambda function.
  assert sum_positivenum([2, 4, -6, -9, 11, -12, 14, -5, 17])==48
  assert sum_positivenum([10,15,-14,13,-18,12,-20])==50
  assert sum_positivenum([19, -65, 57, 39, 152,-639, 121, 44, 90, -190])==522
output: def sum_positivenum(lst):
      return sum(filter(lambda x: x > 0, lst))