import tkinter as tk
from random import randint

def spawn_rectangle() :
    lst = ["red", "blue", "green", "yellow", "grey"]
    indice_couleur = randint(0, len(lst)-1)
    couleur = lst[indice_couleur]
    taille = randint(10, 30)
    position_x = randint(0, 400)
    position_y = randint(0, 300)
    while position_x+taille > 400 or position_y+taille > 300:
        taille = randint(10, 31)
        position_x = randint(0, 400)
        position_y = randint(0, 300)
    rectangle = canva.create_rectangle(position_x, position_y, position_x+taille,
                                       position_y+taille, fill = couleur)

fenetre = tk.Tk()

canva = tk.Canvas(fenetre, width = 400, height = 300, bg = "white")
canva.grid()

Dessin = tk.Button(fenetre, text = "Dessine", command = spawn_rectangle).grid()

fenetre.mainloop()