As a general rule, you shouldn't be calling sleep
in a GUI, and you shouldn't have loops that update the display. If you're periodically updating the display, proper use of after
makes a loop unnecessary.
The general idea is to write a function that does a single update (ie: what you would otherwise have as the body of a loop). Then, have that function call itself via after
.
Here's an example where you can see a bar chart grow over time, without using a loop:
import Tkinter as tk
class Example(tk.Frame):
def __init__(self, parent):
tk.Frame.__init__(self, parent)
self.canvas = tk.Canvas(self)
self.start_button = tk.Button(self, text="start", command=self.on_start)
self.stop_button = tk.Button(self, text="stop", command=self.on_stop)
self.start_button.pack()
self.stop_button.pack()
self.canvas.pack(fill="both", expand=True)
# call on_stop to initialize the state of the buttons
self.on_stop()
def on_start(self):
"""Start the animation"""
self.canvas.delete("all")
self.rect_id = self.canvas.create_rectangle(0,0,1,20, fill="blue")
self.running = True
self.start_button.configure(state="disabled")
self.stop_button.configure(state="normal")
self.draw_one_frame()
def on_stop(self):
"""Stop the animation"""
self.start_button.configure(state="normal")
self.stop_button.configure(state="disabled")
self.running = False
def draw_one_frame(self):
"""Draw a single frame of animation"""
(x0, y0, x1, y1) = self.canvas.coords(self.rect_id)
if x1 < self.canvas.winfo_width():
x1 += 1
else:
x1 = 1
self.canvas.coords(self.rect_id, (x0, y0, x1, y1))
if self.running:
self.after(10, self.draw_one_frame)
if __name__ == "__main__":
root = tk.Tk()
Example(root).pack(fill="both", expand=True)
root.mainloop()
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