ERROR：

ValueError: '\xe5\x94\x90\xe6\x9e\x9c' has type bytes, but isn't in 7-bit ASCII encoding. Non-ASCII strings must be converted to unicode objects before being added.

def StringDecoder(field_number, is_repeated, is_packed, key, new_default):

  """Returns a decoder for a string field."""

  local_DecodeVarint = _DecodeVarint

  local_unicode = unicode

  def _ConvertToUnicode(byte_str):

    try:

      #return local_unicode(byte_str, 'utf-8') # 注释掉 不转码

      return byte_str

    except UnicodeDecodeError, e:

      # add more information to the error message and re-raise it.

      e.reason = '%s in field: %s' % (e, key.full_name)

      raise

class UnicodeValueChecker(object):

  """Checker used for string fields.

  Always returns a unicode value, even if the input is of type str.

  """

  def CheckValue(self, proposed_value):

    if not isinstance(proposed_value, (bytes, unicode)):

      message = ('%.1024r has type %s, but expected one of: %s' %

                 (proposed_value, type(proposed_value), (bytes, unicode)))

      raise TypeError(message)

    # If the value is of type 'bytes' make sure that it is in 7-bit ASCII

    # encoding.

#    if isinstance(proposed_value, bytes):

#      try:

#        proposed_value = proposed_value.decode('ascii')

#      except UnicodeDecodeError:

#        raise ValueError('%.1024r has type bytes, but isn\'t in 7-bit ASCII '

#                         'encoding. Non-ASCII strings must be converted to '

#                         'unicode objects before being added.' %

#                         (proposed_value))

    return proposed_value