input: Write a function that employs a lambda expression to compute the sum of the positive integers from a provided list of values.
  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))