import tkinter as tk
import matplotlib.pyplot as plt

def modif():
    x = float(entry.get())
    lbl.configure(text="x vaut "+str(x))
    plt.scatter(x, x)
    plt.show()

fen = tk.Tk()
lbl = tk.Label(fen, text="Le texte initial")
lbl.grid()
entry = tk.Entry()
entry.grid()
b1 = tk.Button(fen, text="bouton 1", command=modif)
b1.grid()

fig = plt.figure()
plt.xlim(-5,5)
plt.ylim(-5,5)

fen.mainloop()