Error when attempting to create Python GUI using Tkinter: "no display name and no $DISPLAY environment variable"

Question

Sup,

• I am simply trying to use Tkinter (a Python GUI creator) to create a GUI on my Raspberry Pi.
• To start, I only want a GUI to show up on my screen. That's it!
• The code DOES work on my PC
• The code does NOT work on my Raspberry Pi

The entire script looks as follows:
(works on my PC, bringing up an empty GUI)

import Tkinter

root = Tkinter.Tk()

root.mainloop()

Trying to run the program in terminal as follows:

sudo python GUI.py

Produces the following error:

Traceback (most recent call last):

File "GUI.py", line 4, in root = Tkinter.Tk()

File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 1817, in init

self.tk = _tkinter.create(screenName, baseName, className, interactive, wantobjects, useTk, sync, use)

_tkinter.TclError: no display name and no $DISPLAY environment variable

Does anybody have any idea how I can resolve this issue? The error is produced under all of the following conditions:

• Direct HDMI to computer monitor
• DSI connection to touchscreen LCD
• SSH on computer monitor

For reference, if I type the following into my terminal:

echo $DISPLAY

An empty string gets printed, so I believe therein lies the problem

The following commands don't work either, which might shed light on the problem:

sudo apt-get update

startx

• dhruvvyas90: Why do you need sudo ? Are you calling script from ssh ? If yes, try setting DISPLAY varible by export DISPLAY=:0 and then running it. Hope it helps.
• dsazer25: I am indeed running from SSH but I see the exact same error when I directly hardwire the Pi HDMI into a computer monitor and use a USB keyboard.
• dsazer25: I like your idea and I tried it, but now I receive the error: _tkinter.TclError: couldn't connect to display ":0"
• dhruvvyas90: That's because you're running it without x windows. Log in to raspbian desktop by startx and try doing it.
• dsazer25: executing the command "startx" leads to an error as well. I started fresh on a brand new microSD card; everything worked fine until I started installing software packages, although I'm not sure which one led to the problem. If I figure it out I'll post which software package is the culprit!

Answer 1

I solved it with these two commands:

export DISPLAY=0.0
xhost +

• marciokoko: where did you put these commands?
• Ömer Aba: I run it on raspi terminal
• Shalomi90: DId it work? because it does not work on mine

Answer 2

Here is my solution. This works for SSH terminal, or crontab:

import Tkinter
import sys
import os
if os.environ.get('DISPLAY','') == '':
 print('no display found. Using :0.0')
 os.environ.__setitem__('DISPLAY', ':0.0')
#create main window
master = Tkinter.Tk()
master.title("tester")
master.geometry("300x100")
#make a label for the window
label1 = Tkinter.Label(master, text='Hellooooo')
# Lay out label
label1.pack()
# Run forever!
master.mainloop()

• doplano: FYI for python3 one must instead use import tkinter and besides this solution leads to an error: TclError: couldn't connect to display ":0.0"

Answer 3

you have just to write: export MPLBACKEND="agg"

• Steve Robillard: Where would the OP add this line? What does it do? Where can they find documentation about this? How is this better/different from the other answer?
• Aloha: This is only applicable for matplotlib.