guizero Raspberry Pi: button -> command sequence problems

Question

Required: pressing a button on a guizero App should first set a text value, then perform a function (here a simple time.sleep(); originally a subprocess); after performing the function a result text should be displayed;

#!/usr/bin/python3
# -*- coding: utf-8 -*-

from guizero import App, PushButton, Text
import subprocess
import time

# Action you would like to perform
def counter0():
    global s0
    text0.value = int(text0.value) + 1  # works
    text1.value = s0                    # works

def counter1():
    global s0
    text1.value = s0       # display a status value - but does not (!)
    time.sleep(1)          # originally a subprocess is called here; works
    text1.value = "ready"  # only diplays this after a delay

s0="start something after pressing butt1"

app = App("Hello world", layout="grid")

text0 = Text(app, text="1", align="left", grid=[0,1])
text1 = Text(app, text=s0, align="left",grid=[0,8] )
butt1 = PushButton(app, text="Button", command=counter1, align="left", grid=[0,2])
text0.repeat(10000, counter0)  # Schedule call to counter() every 1000ms

app.display()

Most likely I did not understand the idea behind guizero. Any Ideas how to manage such requrements?

score 1 · Accepted Answer · answered Nov 24 '19 at 14:47

If I understand your question correctly, your specific problem is here:

    text1.value = s0       # display a status value - but does not (!)

This doesn't work because the guizero framework is executing the function synchronously: no other code executes -- including the code to update the display -- until the function has returned.

If you want to:

Display a message before running a command with subprocess
Run some command
Display a message after the command completes

Then you will need to rewrite your logic so that you're app isn't waiting for `counter1 to complete. One option for running code asynchronously is to run it in a separate thread. For example:

from guizero import App, PushButton, Text
import threading
import time


# Action you would like to perform
def counter0():
    global s0
    text0.value = int(text0.value) + 1  # works
    text1.value = s0                    # works


def run_command():
    time.sleep(1)          # originally a subprocess is called here; works
    text1.value = "ready"  # only diplays this after a delay


def counter1():
    global s0
    text1.value = "Running command..."
    threading.Thread(target=run_command).start()


s0 = "start something after pressing butt1"

app = App("Hello world", layout="grid")

text0 = Text(app, text="1", align="left", grid=[0, 1])
text1 = Text(app, text=s0, align="left", grid=[0, 8])
butt1 = PushButton(app, text="Button", command=counter1,
                   align="left", grid=[0, 2])
text0.repeat(10000, counter0)

app.display()

Running the above code will give you the following behavior:

Thank you, larsks, for the fast and very helpful answer. It is exactly what I was looking for. Would be interested to see other methods, but is only to satisfy my curiosity. Your suggested method looks for me easy to understand and comfortably short. (btw: nice animated gif ;c) — peets, Nov 24 '19 at 19:11

guizero Raspberry Pi: button -> command sequence problems

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