path/to/venv/lib/python3.10/site-packages/PIL/GribStubImagePlugin.py

#
# The Python Imaging Library
# $Id$
#
# GRIB stub adapter
#
# Copyright (c) 1996-2003 by Fredrik Lundh
#
# See the README file for information on usage and redistribution.
#
from __future__ import annotations

from . import Image, ImageFile

_handler = None


def register_handler(handler):
    """
    Install application-specific GRIB image handler.

    :param handler: Handler object.
    """
    global _handler
    _handler = handler


# --------------------------------------------------------------------
# Image adapter


def _accept(prefix):
    return prefix[:4] == b"GRIB" and prefix[7] == 1


class GribStubImageFile(ImageFile.StubImageFile):
    format = "GRIB"
    format_description = "GRIB"

    def _open(self):
        offset = self.fp.tell()

        if not _accept(self.fp.read(8)):
            msg = "Not a GRIB file"
            raise SyntaxError(msg)

        self.fp.seek(offset)

        # make something up
        self._mode = "F"
        self._size = 1, 1

        loader = self._load()
        if loader:
            loader.open(self)

    def _load(self):
        return _handler


def _save(im, fp, filename):
    if _handler is None or not hasattr(_handler, "save"):
        msg = "GRIB save handler not installed"
        raise OSError(msg)
    _handler.save(im, fp, filename)


# --------------------------------------------------------------------
# Registry

Image.register_open(GribStubImageFile.format, GribStubImageFile, _accept)
Image.register_save(GribStubImageFile.format, _save)

Image.register_extension(GribStubImageFile.format, ".grib")