invalid command name ".!canvas"

Question

I'm attempting to create a canvas with 100 completely random rectangles appearing, but what I get is a blank canvas and an error:

How do i fix this?

from tkinter import *
import random
tk = Tk()
canvas = Canvas(tk, width=400, height=400)
canvas.pack()
tk.mainloop()

def rndm_rect(width, height):
    x1 = (random.randrange(width))
    y1 = (random.randrange(height))
    x2 = x1 + (random.randrange(width))
    y2 = y1 + (random.randrange(width))
    canvas.create_rectangle(x1, y1, x2, y2)

rndm_rect(400, 400)


for x in range(0, 100):
    rndm_rect(400, 400)

I would also recommend updating your title to an actual question — Ethan Field
– Ethan Field, Commented Aug 4, 2017 at 15:26
It is because tkinter window closed but other processes related to it e.g. canvas.delete('ball') is still running. To avoid this, put try and except when calling animate() function. To avoid the error, import sys and do this whenever animate() is called: try: self.animate() except: sys.exit(1) — Prashant
– Prashant, Commented Jan 26, 2022 at 7:14

Ethan Field · Accepted Answer · 2017-08-07 13:07:40Z

2

tk.mainloop() is the command used to start the event loop, as such you're generating the window before you've declared the variables for the rectangle positions.

Place tk.mainloop() at the end of your script and it runs fine, see below:

from tkinter import *
import random
tk = Tk()
canvas = Canvas(tk, width=400, height=400)
canvas.pack()

def rndm_rect(width, height):
    x1 = (random.randrange(width))
    y1 = (random.randrange(height))
    x2 = x1 + (random.randrange(width))
    y2 = y1 + (random.randrange(width))
    canvas.create_rectangle(x1, y1, x2, y2)

rndm_rect(400, 400)


for x in range(0, 100):
    rndm_rect(400, 400)

tk.mainloop()

edited Aug 7, 2017 at 13:07

answered Aug 4, 2017 at 15:24

Ethan Field

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1 Comment

Bryan Oakley Over a year ago

"tk.mainloop() is the command used to generate the tKinter master window" - that is a false statement. It doesn't create or generate any windows, it simply starts the event loop.

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