Embedding sympy plot in GTK

[mskf1383]

Hi
I try to embed sympy plot in a GTK4 window. This is my code:

import gi
gi.require_version('Gtk', '4.0')
from gi.repository import Gtk

from matplotlib.backends.backend_gtk4agg import (
    FigureCanvasGTK4Agg as FigureCanvas)
from matplotlib.figure import Figure
import numpy as np
from sympy import *


def on_activate(app):
    win = Gtk.ApplicationWindow(application=app)
    win.set_default_size(400, 300)
    win.set_title("Embedding in GTK4")

    x = symbols("x")
    f = x**2 + 3*x - 5
    fig = plot(f)._backend.fig

    # A scrolled margin goes outside the scrollbars and viewport.
    sw = Gtk.ScrolledWindow(margin_top=10, margin_bottom=10,
                            margin_start=10, margin_end=10)
    win.set_child(sw)

    canvas = FigureCanvas(fig)  # a Gtk.DrawingArea
    canvas.set_size_request(800, 600)
    sw.set_child(canvas)

    win.show()


app = Gtk.Application(application_id='org.matplotlib.examples.EmbeddingInGTK4')
app.connect('activate', on_activate)
app.run(None)

The problem is that after running the program, it show a window of plot, then after closing that window, the GTK window with embedded plot shown. And if i set show=False, this error shown:

Traceback (most recent call last):
  File "/home/mskf1383/سندها/پروژه‌ها/python_projects/GTK/mplot.py", line 19, in on_activate
    fig = plot(f, show=False)._backend.fig
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'Plot' object has no attribute '_backend'. Did you mean: 'backend'?

And if I remove ._backend.fig (fig = plot(f, show=False)), this error shown:

Traceback (most recent call last):
  File "/home/mskf1383/سندها/پروژه‌ها/python_projects/GTK/mplot.py", line 26, in on_activate
    canvas = FigureCanvas(fig)  # a Gtk.DrawingArea
             ^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/matplotlib/backends/backend_gtk4.py", line 42, in __init__
    super().__init__(figure=figure)
  File "/usr/lib/python3/dist-packages/matplotlib/backend_bases.py", line 1643, in __init__
    figure.set_canvas(self)
    ^^^^^^^^^^^^^^^^^
AttributeError: 'Plot' object has no attribute 'set_canvas'

How can I fix that?
Thanks!