code: def is_valid_key(key):
      
  
      if PY3 and isinstance(key, bytes):
          raise TypeError("needs to be str not bytes")
  
      for c in key:
          if c < " " or c > "}" or c == "=":
              return False
      else:
          return bool(key)
docs: Return true if a string is a valid Vorbis comment key.
  
      Valid Vorbis comment keys are printable ASCII between 0x20 (space)
      and 0x7D ('}'), excluding '='.
  
      Takes str/unicode in Python 2, unicode in Python 3