matplotlib/matplotlib · error · ValueError

Unknown vf opcode {byte}

Error message

Unknown vf opcode {byte}

What it means

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

Source

Thrown at lib/matplotlib/dviread.py:919

                c = self._read_arg(4)
                s = self._read_arg(4)
                d = self._read_arg(4)
                a = self._read_arg(1)
                l = self._read_arg(1)
                self._fnt_def_real(k, c, s, d, a, l)
                if self._first_font is None:
                    self._first_font = k
            elif byte == 247:       # preamble
                i = self._read_arg(1)
                k = self._read_arg(1)
                x = self.file.read(k)
                cs = self._read_arg(4)
                ds = self._read_arg(4)
                self._pre(i, x, cs, ds)
            elif byte == 248:       # postamble (just some number of 248s)
                break
            else:
                raise ValueError(f"Unknown vf opcode {byte}")

    def _init_packet(self, pl):
        if self.state != _dvistate.outer:
            raise ValueError("Misplaced packet in vf file")
        self.h = self.v = self.w = self.x = self.y = self.z = 0
        self.stack = []
        self.text = []
        self.boxes = []
        self.f = self._first_font
        self._missing_font = None
        return self.file.tell() + pl

    def _finalize_packet(self, packet_char, packet_width):
        if not self._missing_font:  # Otherwise we don't have full glyph definition.
            self._chars[packet_char] = Page(
                text=self.text, boxes=self.boxes, width=packet_width,
                height=None, descent=None)
        self.state = _dvistate.outer

View on GitHub (pinned to b379c1b69e)

When it happens

Trigger: Thrown at lib/matplotlib/dviread.py:919 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/c91794a491bd13f6. Report an issue: GitHub.