matplotlib/matplotlib · error · ValueError

Inappropriate opcode {byte} in vf file

Error message

Inappropriate opcode {byte} in vf file

What it means

Error "Inappropriate opcode {byte} in vf file" thrown in matplotlib/matplotlib.

Source

Thrown at lib/matplotlib/dviread.py:883

        Read one page from the file. Return True if successful,
        False if there were no more pages.
        """
        packet_char = packet_ends = None
        packet_len = packet_width = None
        while True:
            byte = self.file.read(1)[0]
            # If we are in a packet, execute the dvi instructions
            if self.state is _dvistate.inpage:
                byte_at = self.file.tell()-1
                if byte_at == packet_ends:
                    self._finalize_packet(packet_char, packet_width)
                    packet_len = packet_char = packet_width = None
                    # fall through to out-of-packet code
                elif byte_at > packet_ends:
                    raise ValueError("Packet length mismatch in vf file")
                else:
                    if byte in (139, 140) or byte >= 243:
                        raise ValueError(f"Inappropriate opcode {byte} in vf file")
                    Dvi._dtable[byte](self, byte)
                    continue

            # We are outside a packet
            if byte < 242:          # a short packet (length given by byte)
                packet_len = byte
                packet_char = self._read_arg(1)
                packet_width = self._read_arg(3)
                packet_ends = self._init_packet(byte)
                self.state = _dvistate.inpage
            elif byte == 242:       # a long packet
                packet_len = self._read_arg(4)
                packet_char = self._read_arg(4)
                packet_width = self._read_arg(4)
                self._init_packet(packet_len)
            elif 243 <= byte <= 246:
                k = self._read_arg(byte - 242, byte == 246)
                c = self._read_arg(4)

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/dviread.py:883 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of matplotlib/matplotlib@b379c1b69e (2026-08-21). Data as JSON: /api/errors/4ab794b14b551ff4. Report an issue: GitHub.