Tkinter window is blank when running

it is because you are not packing it in the window but you are printing it in the python shell.

you should replace that print newtext with:

w = Label(root, text=newtext)w.pack() 

a working code should look like this:

#!/usr/bin/python# -*- coding: latin-1 -*-import Adafruit_DHT as dhtimport timefrom Tkinter import *root = Tk()k= StringVar()num = 1thelabel = Label(root, textvariable=k)thelabel.packdef READ():    h,t = dht.read_retry(dht.DHT22, 4)    newtext = "Temp=%s*C Humidity=%s" %(t,h)    k.set(str(newtext))    w = Label(root, text=newtext)    w.pack() def read30seconds():    READ()    root.after(30000, read30seconds)read30seconds()root.mainloop()

note that this is a very basic code graphically speaking.to learn more about this topic visit this tkinter label tutorialand to learn more about tkinter itself visit this introduction to tkinter

if you want the label to be overwritten everytime it is refreshed you should use the destroy() method to delete and then replace the Label like this:

#!/usr/bin/python# -*- coding: latin-1 -*-import Adafruit_DHT as dhtimport timefrom Tkinter import *root = Tk()k= StringVar()num = 1thelabel = Label(root, textvariable=k)thelabel.packdef READ():    global w    h,t = dht.read_retry(dht.DHT22, 4)    newtext = "Temp=%s*C Humidity=%s" %(t,h)    k.set(str(newtext))    print newtext #I added this line to make sure that newtext actually had the values I wanteddef read30seconds():    READ()    try: w.destroy()    except: pass    root.after(30000, read30seconds)read30seconds()root.mainloop()