code: def join(items, separator=None):
      
      if not items:
          return ''
      if separator is None:
          separator = _default_separator()
      return separator.join([str(item) for item in items])
docs: Join the items into a string using the separator
  
      Converts items to strings if needed
  
      >>> join([1, 2, 3])
      '1,2,3'