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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fetch(self, x, y, w, h):
 """Fill a region with pixel data. Pixels are filled with data! Returns: Pixel data. Raises: :class:`.Error` """


        if not at_least_libvips(8, 8):
            raise Error('libvips too old')

        psize = ffi.new('size_t *')
        pointer = vips_lib.vips_region_fetch(self.pointer, x, y, w, h, psize)
        if pointer == ffi.NULL:
            raise Error('unable to fetch from region')

        pointer = ffi.gc(pointer, glib_lib.g_free)
        return ffi.buffer(pointer, psize[0])