{"record":{"id":"4ab794b14b551ff4","repo":"matplotlib/matplotlib","slug":"inappropriate-opcode-byte-in-vf-file","errorCode":null,"errorMessage":"Inappropriate opcode {byte} in vf file","messagePattern":"Inappropriate opcode (.+?) in vf file","errorType":"exception","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"lib/matplotlib/dviread.py","lineNumber":883,"sourceCode":"        Read one page from the file. Return True if successful,\n        False if there were no more pages.\n        \"\"\"\n        packet_char = packet_ends = None\n        packet_len = packet_width = None\n        while True:\n            byte = self.file.read(1)[0]\n            # If we are in a packet, execute the dvi instructions\n            if self.state is _dvistate.inpage:\n                byte_at = self.file.tell()-1\n                if byte_at == packet_ends:\n                    self._finalize_packet(packet_char, packet_width)\n                    packet_len = packet_char = packet_width = None\n                    # fall through to out-of-packet code\n                elif byte_at > packet_ends:\n                    raise ValueError(\"Packet length mismatch in vf file\")\n                else:\n                    if byte in (139, 140) or byte >= 243:\n                        raise ValueError(f\"Inappropriate opcode {byte} in vf file\")\n                    Dvi._dtable[byte](self, byte)\n                    continue\n\n            # We are outside a packet\n            if byte < 242:          # a short packet (length given by byte)\n                packet_len = byte\n                packet_char = self._read_arg(1)\n                packet_width = self._read_arg(3)\n                packet_ends = self._init_packet(byte)\n                self.state = _dvistate.inpage\n            elif byte == 242:       # a long packet\n                packet_len = self._read_arg(4)\n                packet_char = self._read_arg(4)\n                packet_width = self._read_arg(4)\n                self._init_packet(packet_len)\n            elif 243 <= byte <= 246:\n                k = self._read_arg(byte - 242, byte == 246)\n                c = self._read_arg(4)","sourceCodeStart":865,"sourceCodeEnd":901,"githubUrl":"https://github.com/matplotlib/matplotlib/blob/b379c1b69e012b142c0f496a52bcb30513802d72/lib/matplotlib/dviread.py#L865-L901","documentation":"Error \"Inappropriate opcode {byte} in vf file\" thrown in matplotlib/matplotlib.","triggerScenarios":"Thrown at lib/matplotlib/dviread.py:883 when the library encounters an invalid state.","commonSituations":"See trigger scenarios.","solutions":[],"exampleFix":null,"handlingStrategy":null,"validationCode":null,"typeGuard":null,"tryCatchPattern":null,"preventionTips":[],"tags":[],"backgroundTag":null,"analyzedSha":"b379c1b69e012b142c0f496a52bcb30513802d72","analyzedAt":"2026-08-21T23:31:55.468Z","schemaVersion":2},"datasetVersion":"2026-08-22T04:17:13.399Z"}