input: Write a function to print the length of a given string. The function should return the length of the string as an integer. If the given string is empty, the function should return 0.
  def string_length(s):
      if s == "":
          return 0
      return len(s)
  assert string_length("Python")==6
  assert string_length("Hello, World!")==13
  assert string_length("")==0
  assert string_length("123456")==6
output: def string_length(s):
      if s == "":
          return 0
      return len(s)