connections.py 文件源码

def _get_descriptions(self):
        """Read a column descriptor packet for each column in the result."""
        self.fields = []
        self.converters = []
        use_unicode = self.connection.use_unicode
        conn_encoding = self.connection.encoding
        description = []

        for i in range_type(self.field_count):
            field = self.connection._read_packet(FieldDescriptorPacket)
            self.fields.append(field)
            description.append(field.description())
            field_type = field.type_code
            if use_unicode:
                if field_type == FIELD_TYPE.JSON:
                    # When SELECT from JSON column: charset = binary
                    # When SELECT CAST(... AS JSON): charset = connection encoding
                    # This behavior is different from TEXT / BLOB.
                    # We should decode result by connection encoding regardless charsetnr.
                    # See https://github.com/PyMySQL/PyMySQL/issues/488
                    encoding = conn_encoding  # SELECT CAST(... AS JSON) 
                elif field_type in TEXT_TYPES:
                    if field.charsetnr == 63:  # binary
                        # TEXTs with charset=binary means BINARY types.
                        encoding = None
                    else:
                        encoding = conn_encoding
                else:
                    # Integers, Dates and Times, and other basic data is encoded in ascii
                    encoding = 'ascii'
            else:
                encoding = None
            converter = self.connection.decoders.get(field_type)
            if converter is through:
                converter = None
            if DEBUG: print("DEBUG: field={}, converter={}".format(field, converter))
            self.converters.append((encoding, converter))

        eof_packet = self.connection._read_packet()
        assert eof_packet.is_eof_packet(), 'Protocol error, expecting EOF'
        self.description = tuple(description)