如何从Python中的函数外部更改标签文本

Question

I'm new to programming and I'm trying to make something as simple as displaying the temperature. I can't get the temperature to display until I close the window, it goes into the loop get_outside_temp() but doesn't display anything until I break the loop then the window will be drawn. See code below.

 #Import needed files
import tkinter as tk
import sys
import time


#define some variables
green = '#2BF720'
blue='#0CCAF0'
#blue = '#427BED'
font10 = "-family Newspaper -size 18 -weight bold -slant roman -underline 0 -overstrike 0"
font2 = "-family Newspaper -size 36 -weight bold -slant roman -underline 0 -overstrike 0"

#get outside temp and display it
def get_outside_temp():
     while True:
        tfile = open("/sys/bus/w1/devices/28-0416b113e1ff/w1_slave") 
        text = tfile.read() 
        tfile.close() 
        secondline = text.split("\n")[1] 
        temperaturedata = secondline.split(" ")[9] 
        outside_temp = float(temperaturedata[2:]) 
        outside_temp = round(outside_temp / 1000 ,1)
        print(outside_temp) #so I can see it's working
        #this is wherre I'm trying to display the temperature in the window.
        outside_temp_label.config(text = outside_temp)
        '''
        outside_temp_label = tk.Label(outside_frame, text=outside_temp, bg="Black", fg='White', font=font2)
        outside_temp_label.grid(padx=140, pady=75)
        '''
        time.sleep(5)


#create main window
root = tk.Tk()
root.geometry("800x480")
root.configure(bg="black")
root.title("Go Nad Go IV")

#create the frame for the outside
outside_frame = tk.Frame(root, height=230, width = 390, bg="black", 
relief="groove", highlightcolor = blue, highlightbackground=blue, highlightthickness = 2)
outside_frame.grid(row=0, column=1, padx=5, pady=5)
outside_frame.grid_propagate(False)
outside_label = tk.Label(outside_frame, text="Outside Temperature", bg="Black", fg=blue, font=font10)
outside_label.grid(column=0,row=0)

#get the outside temp
tfile = open("/sys/bus/w1/devices/28-0416b113e1ff/w1_slave") 
text = tfile.read()
tfile.close() 
secondline = text.split("\n")[1] 
temperaturedata = secondline.split(" ")[9] 
outside_temp = float(temperaturedata[2:]) 
outside_temp = round(outside_temp / 1000 ,1)

#display the temp
outside_temp_label = tk.Label(outside_frame, text=outside_temp, bg="Black", fg='White', font=font2)
outside_temp_label.grid(padx=140, pady=75)

get_outside_temp()
root.mainloop()

Answer 1

Your problem isn't with accessing the label, it's that your entire program is unresponsive for 5 seconds during that time.sleep(5) . So, you've updated the label in memory, but it doesn't redrawn on the screen, because nothing at all is getting redrawn.

You can't sleep in a GUI program. If you want something to run every 5 seconds, you have three choices: use a background thread, drive the event loop manually, or just ask the GUI to run your code again in 5 seconds.

The last one is by far the simplest. In tkinter, it's spelled after , and you use it like this:

def get_outside_temp():

    # No while True loop here!

    tfile = open("/sys/bus/w1/devices/28-0416b113e1ff/w1_slave") 
    text = tfile.read() 
    tfile.close() 

    # all your other existing code, except the sleep

    root.after(5000, callback=get_outside_temp)

In other words, instead of a function that runs forever, sleeping for 5 seconds at a time, we have a function that runs really quickly, asks to get run again in 5 seconds, and then returns to the event loop so other stuff can run (like redrawing the screen, responding to the mouse, etc.).

Answer 2

Thanks, I did manage to get it to work.
Instead of: root.after(5000, callback=get_outside_temp) I had to use: root.after(5000, get_outside_temp)