code: def seq_to_str(obj, sep=","):
      
      if isinstance(obj, string_classes):
          return obj
      elif isinstance(obj, (list, tuple)):
          return sep.join([str(x) for x in obj])
      else:
          return str(obj)
docs: Given a sequence convert it to a comma separated string.
      If, however, the argument is a single object, return its string
      representation.