We will take the code sample from the Drawing lines and arrows recipe to add a button to print the canvas contents to a PostScript file:

import tkinter as tk

class App(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title("Basic canvas")

        self.line_start = None
        self.form = LineForm(self)
        self.render_btn = tk.Button(self, text="Render canvas",
                                    command=self.render_canvas)
        self.canvas = tk.Canvas(self, bg="white")
        self.canvas.bind("<Button-1>", self.draw)

        self.form.grid(row=0, column=0, padx=10, pady=10)
        self.render_btn.grid(row=1, column=0)
        self.canvas.grid(row=0, column=1, rowspan=2)

    def draw(self, event):
        # ...

    def render_canvas(self):
        self.canvas.postscript(file="output.ps", colormode="color")