input: Write a python function to classify numbers as positive or negative.
  assert classify(5) == 'positive'
  assert classify(-3) == 'negative'
  assert classify(0) == 'negative'
  assert classify(100) == 'positive'
  assert classify(-50) == 'negative'
output: def classify(number):
      if number > 0:
          return 'positive'
      else:
          return 'negative'