How to use the pyvips._to_bytes function in pyvips

The metadata item as a Python value.

        Raises:
            :class:`.Error`

        """

        # with old libvips, we must fetch properties (as opposed to
        # metadata) via VipsObject
        if not at_least_libvips(8, 5):
            gtype = super(Image, self).get_typeof(name)
            if gtype != 0:
                return super(Image, self).get(name)

        gv = GValue()
        result = vips_lib.vips_image_get(self.pointer, _to_bytes(name),
                                         gv.pointer)
        if result != 0:
            raise Error('unable to get {0}'.format(name))

        return gv.get()

def _get_pspec(self, name):
        # logger.debug('VipsObject.get_typeof: self = %s, name = %s',
        #              str(self), name)

        pspec = ffi.new('GParamSpec **')
        argument_class = ffi.new('VipsArgumentClass **')
        argument_instance = ffi.new('VipsArgumentInstance **')
        result = vips_lib.vips_object_get_argument(self.vobject,
                                                   _to_bytes(name),
                                                   pspec, argument_class,
                                                   argument_instance)

        if result != 0:
            return None

        return pspec[0]

def set_string(self, string_options):
        """Set a series of properties using a string.

        For example::

            'fred=12, tile'
            '[fred=12]'

        """

        cstr = _to_bytes(string_options)
        result = vips_lib.vips_object_set_from_string(self.vobject, cstr)

        return result == 0

def new_from_file(filename):
        """Make a new stream from a filename.

        Make a new stream that is attached to the named file. For example::

            streami = pyvips.Streami.new_from_file("myfile.jpg")

        You can pass this stream to (for example) :meth:`new_from_stream`.

        """

        # logger.debug('VipsStreami.new_from_file: filename = %s',
        #              filename)

        pointer = vips_lib.vips_streami_new_from_file(_to_bytes(filename))
        if pointer == ffi.NULL:
            raise Error("can't create input stream from filename {0}"
                        .format(filename))

        return Streami(pointer)

The value of the property is converted to a Python value.

        """

        logger.debug('VipsObject.get: name = %s', name)

        pspec = self._get_pspec(name)
        if pspec is None:
            raise Error('Property not found.')
        gtype = pspec.value_type

        gv = pyvips.GValue()
        gv.set_type(gtype)
        go = ffi.cast('GObject *', self.pointer)
        gobject_lib.g_object_get_property(go, _to_bytes(name), gv.pointer)

        return gv.get()

JPEG saver.

        Args:
            streamo (Streamo): The stream to write the image to
            format_string (str): The suffix, plus any string-form arguments.

        Other arguments depend upon the save operation.

        Returns:
            None

        Raises:
            :class:`.Error`

        """
        format_string = _to_bytes(format_string)

        pointer = vips_lib.vips_filename_get_options(format_string)
        options = _to_string_copy(pointer)

        pointer = vips_lib.vips_foreign_find_save_stream(format_string)
        if pointer == ffi.NULL:
            raise Error('unable to write to stream')
        name = _to_string(pointer)

        return pyvips.Operation.call(name, self, streamo,
                                     string_options=options, **kwargs)

Fetch the GType of a piece of metadata, or 0 if the named item does not
        exist. See :class:`GValue`.

        Args:
            name (str): The name of the piece of metadata to get the type of.

        Returns:
            The ``GType``, or 0.

        Raises:
            None

        """

        return vips_lib.vips_image_get_typeof(self.pointer, _to_bytes(name))

"""Remove an item of metadata.

        The named metadata item is removed.

        Args:
            name (str): The name of the piece of metadata to remove.

        Returns:
            None

        Raises:
            None

        """

        return vips_lib.vips_image_remove(self.pointer, _to_bytes(name)) != 0