tkinter: How can I use one vertical scroll bar to scroll two canvases?

Question

In my UI I need two canvases, each with their own horizontal scroll bar, but with a single scroll bar controlling the vertical movement of both canvases.

The following code creates two canvases, each with their own horizontal and vertical scrollbars. How can I get rid of one of the vertical scrollbars? Apologies for the length of code, it's as canonical as I could make it.

from tkinter import *
from tkinter import ttk

class MainUI:
    def __init__(self, root):

        mainframe = Frame(root)
        mainframe.grid(column=0, row=0, sticky=(N,W,E,S))

        # set up the first canvas, with large red triangle
        canvas1 = Canvas(mainframe, background="turquoise")
        canvas1.grid(column=1, row=1, sticky=(N,S,W,E))

        canvas1_hscroller = Scrollbar(mainframe, orient="horizontal",command=canvas1.xview)
        canvas1_hscroller.grid(column=1, row=2, sticky=(W,E))
        canvas1.configure(xscrollcommand=canvas1_hscroller.set)

        canvas1_vscroller = Scrollbar(mainframe, orient="vertical",command=canvas1.yview)
        canvas1_vscroller.grid(column=2, row=1, sticky=(N,S))
        canvas1.configure(yscrollcommand=canvas1_vscroller.set)

        points = [0,0,1000,800,800,1000]
        triangle = canvas1.create_polygon(points,fill="red")

        canvas1.configure(scrollregion=canvas1.bbox("all"))

        # set up the second canvas, with large green triangle
        canvas2 = Canvas(mainframe, background="orange")
        canvas2.grid(column=3, row=1, sticky=(N,S,W,E))

        canvas2_hscroller = Scrollbar(mainframe, orient="horizontal",command=canvas2.xview)
        canvas2_hscroller.grid(column=3, row=2, sticky=(W,E))
        canvas2.configure(xscrollcommand=canvas2_hscroller.set)

        canvas2_vscroller = Scrollbar(mainframe, orient="vertical",command=canvas2.yview)
        canvas2_vscroller.grid(column=4, row=1, sticky=(N,S))
        canvas2.configure(yscrollcommand=canvas2_vscroller.set)

        points = [0,0,1000,800,800,1000]
        triangle = canvas2.create_polygon(points,fill="green")

        canvas2.configure(scrollregion=canvas2.bbox("all"))

root = Tk()
ui = MainUI(root)
root.mainloop()

Answer 1

First make the canvases attributes of the instance:

...
self.canvas1 = Canvas(mainframe, background="turquoise")
...
self.canvas2 = Canvas(mainframe, background="orange")

and use the self. prefix everywhere where you reference previously canvas1 and canvas2

Then define a new method

def v_scroll(self, *args):
    self.canvas1.yview(*args)
    self.canvas2.yview(*args)

Then just set the scrollbar command to that method:

canvas_vscroller = Scrollbar(..., command=self.v_scroll)

Additionally, don't use from tkinter import * , it is bad practice to use * when importing modules. Import only what you need. For example in this case

from tkinter import Tk, Frame, Canvas, Scrollbar