如何在没有外部依赖的情况下使用Python在Linux中捕获屏幕截图？

<code class="python">import gtk.gdk

# Fetch desktop window information
w = gtk.gdk.get_default_root_window()
sz = w.get_size()

# Create a pixbuf for capturing the screen
pb = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB, False, 8, sz[0], sz[1])
pb = pb.get_from_drawable(w, w.get_colormap(), 0, 0, 0, 0, sz[0], sz[1])

# Check if the pixbuf is successfully captured
if pb is not None:
    save_path = "screenshot.png"
    print(f"Screenshot saved to {save_path}.")
    pb.save(save_path, "png")
else:
    print("Unable to capture the screenshot. Retry the operation.")</code>