Simulate keystroke in Raspbian with python

Question

I stumbled upon this question when trying to figure out how to get a python script to send a left or right keystroke after button presses (utilizing the GPIO pins).

It seems like the chosen answer to the linked question is what I need to get me going but after installing xautomation, trying to adapt the code to my script and reading up on the documentation for Popen (I even tried running a new file with the code verbatim) I keep getting the following error:

Traceback (most recent call last):
  File "/home/zdistaging/Documents/xte test.py", line 17, in <module>
    keypress(shift_a_sequence)
  File "/home/zdistaging/Documents/xte test.py", line 15, in keypress
    p.communicate(input=sequence)
  File "/usr/lib/python3.4/subprocess.py", line 941, in communicate
    self.stdin.write(input)
TypeError: 'str' does not support the buffer interface

I'm running Python3 on a Pi 3 model B, in Raspbian Jessie with Pixel (downloaded from raspberrypi.org)

Any ideas why it's erroring out?

If it helps at all, all I'm trying to do is allow a user to scroll left and right in a FEH slideshow... I might be totally off the mark with this approach given how seemingly simple a task this is. I'm not looking for someone to solve this for me outright - I like the challenge associated with coding - I'm just super new to python; nudging me in the right direction would be super helpful.

Any help is greatly appreciated!!!

EDIT: Sorry about not including the code!

from subprocess import Popen, PIPE

control_f4_sequence = '''keydown Control_L
key F4
keyup Control_L
'''

shift_a_sequence = '''keydown Shift_L
key A
keyup Shift_L
'''

def keypress(sequence):
    p = Popen(['xte'], stdin=PIPE)
    p.communicate(input=sequence)

keypress(shift_a_sequence)
keypress(control_f4_sequence)

EDIT EDIT:

Here's my updated code... it actually prints spaces for both left and right button presses.

import time
import RPi.GPIO as GPIO
from subprocess import Popen, PIPE
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

leftArrow = '''key \x1B[D'''  # I've tried '''key Left'''
rightArrow = '''key \x1B[C''' # and '''key Right''' with the same results

offButton   = 26     # Black wire
onButton    = 19     # White wire
leftButton  = 13     # Red wire
rightButton =  6     # Green wire


def keypress(sequence):
    if isinstance(sequence, str):
        sequence = sequence.encode('ascii')
    p = Popen(['xte'], stdin=PIPE)
    p.communicate(input=sequence)


GPIO.setup( offButton, GPIO.IN, GPIO.PUD_UP )
GPIO.setup( onButton, GPIO.IN, GPIO.PUD_UP )
GPIO.setup( leftButton, GPIO.IN, GPIO.PUD_UP )
GPIO.setup( rightButton, GPIO.IN, GPIO.PUD_UP )


while True:
    offButton_state = GPIO.input( offButton )
    onButton_state = GPIO.input( onButton )
    leftButton_state = GPIO.input( leftButton )
    rightButton_state = GPIO.input( rightButton )

    if offButton_state == GPIO.LOW:
        print( "Off button pressed" )

    if onButton_state == GPIO.LOW:
        print( "On button pressed" )

    if leftButton_state == GPIO.LOW:
        keypress(leftArrow)
        print( "Left button pressed" )

    if rightButton_state == GPIO.LOW:
        keypress(rightArrow)
        print( "Right button pressed" )

    time.sleep( 1 )

I've read up on subprocess and Popen.communicate() but couldn't really tell if the problem had something to do with that or with what xte is expecting as an argument. Thoughts?

Please add the related code to your question! – Klaus D. Mar 09 '17 at 06:11 — Klaus D., Mar 09 '17 at 06:11

score 1 · Answer 1 · answered Mar 09 '17 at 06:35

1

The error indicates that your control sequences are strings (i.e. unicode), but Subprocess seems to expect bytes.

In function keypress, convert the sequence into bytes like so:

if isinstance(sequence, str):
    sequence = sequence.encode('ascii')

A very good writeup about bytes, strings, and unicode can be found here: https://nedbatchelder.com/text/unipain.html

answered Mar 09 '17 at 06:35

Torben Klein

2,943
1
19
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Holy cow!!! That worked like a charm, thanks so much!!! It is doing something weird though... even though I defined different sequences for the left and right arrows, both are giving me spaces. – A.C. Mar 10 '17 at 21:58
Also, that's an awesome writeup, thanks for sharing! – A.C. Mar 10 '17 at 21:59

score 0 · Answer 2 · answered May 31 '17 at 00:18

I've been looking at the same examples, here's my working example for 6 buttons: (it's somewhat messy, but my debug lines might help others too)

import time
import RPi.GPIO as GPIO
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)
from Xlib import X
from subprocess import Popen, PIPE

buttons = [18,         23,         24,         25,        8,     7 ]
opcodes = ['next', 'enter', 'alt tab', 'previous', 'spacebar', 'shift' ]
opcodes2 = ['key Left ', 'key Up ', 'key Down ', 'key Right ', 'key Enter ', 'key Shift_L ']

# set the gpio pins 
for button in buttons:
    GPIO.setup(button, GPIO.IN, GPIO.PUD_UP )

def keypress(sequence):
    #if isinstance(sequence, str):
    #sequence = sequence.encode('ascii')
    p = Popen(['xte', '-x:0'], stdin=PIPE)
    p.communicate(input=sequence)

def main():
    while True:
        button_state = []
        for button in buttons:
            button_state.append(GPIO.input(button))

        for item in range(len(button_state)):
            if button_state[item] == 0:
                print (opcodes2[item] ) #debugging
           # send X key for keystroke in (for the given iteration of the loop) opcodes[button.output(index)]
                #print (repr(str(opcodes2[item]).encode('ascii')))
                keypress(str(opcodes2[item]).encode('ascii'))
        print (repr(button_state)) #for debugging
        time.sleep(0.3)
        del button_state

if __name__ == '__main__':
    main()

note the trailing whitespace (could be any char) within opcodes2 per command. the ascii encode was dropping the last character on me, so this is my somewhat ugly workaround.

Simulate keystroke in Raspbian with python

2 Answers2