如何从textview计算字体大小？

Question

如何从textview计算字体大小？你知道吗

更改字体大小的应用程序：

def on_scroll(self, widget, event):
    """ handles on scroll event"""

    # Handles zoom in / zoom out on Ctrl+mouse wheel

    size = 12
    accel_mask = Gtk.accelerator_get_default_mod_mask()
    if event.state & accel_mask == Gdk.ModifierType.CONTROL_MASK:
        direction = event.get_scroll_deltas()[2]
        if direction > 0:  # scrolling down -> zoom out
            size -= 2
            font_size = Pango.FontDescription(str(size))
            self.textview.modify_font(font_size)
            print("w dół")
        elif direction < 0:
            direction += 0.1
            size *= 2
            font_size = Pango.FontDescription(str(size))
            self.textview.modify_font(font_size)
            print("do góry")