Pygame PiTFT touch events - main loop sits waiting until touches are detected - raspberry-pi

Question

I am using a raspberry pi and PiTFT to measure sensors and display the results.
Using the tips from https://stackoverflow.com/a/54986161 all is working fine but one problem:
the main loop sits waiting until the lcd is touched.
I removed all non trivial parts from the program just to test the main loop.
This piece of code is printing the state after touch and release.
As long as the lcd is being touched the main loop keeps printing, releasing the lcd stops the loop. How can I rewrite the loop so it's keeps running even when there is no keypress?
#!/usr/bin/python3
import subprocess, pygame, evdev, select
pygame.init()
surfaceSize = (320, 240)
##
# Everything that follows is for handling the touchscreen touch events via evdev
##
# Used to map touch event from the screen hardware to the pygame surface pixels.
# (Those values have been found empirically, but I'm working on a simple interactive calibration tool
tftOrig = (3750, 180)
tftEnd = (150, 3750)
tftDelta = (tftEnd [0] - tftOrig [0], tftEnd [1] - tftOrig [1])
tftAbsDelta = (abs(tftEnd [0] - tftOrig [0]), abs(tftEnd [1] - tftOrig [1]))
# We use evdev to read events from our touchscreen
# (The device must exist and be properly installed for this to work)
touch = evdev.InputDevice('/dev/input/touchscreen')
# We make sure the events from the touchscreen will be handled only by this program
# (so the mouse pointer won't move on X when we touch the TFT screen)
touch.grab()
# Prints some info on how evdev sees our input device
print(touch)
# Even more info for curious people
#print(touch.capabilities())
# Here we convert the evdev "hardware" touch coordinates into pygame surface pixel coordinates
def getPixelsFromCoordinates(coords):
# TODO check divide by 0!
if tftDelta [0] < 0:
x = float(tftAbsDelta [0] - coords [0] + tftEnd [0]) / float(tftAbsDelta [0]) * float(surfaceSize [0])
else:
x = float(coords [0] - tftOrig [0]) / float(tftAbsDelta [0]) * float(surfaceSize [0])
if tftDelta [1] < 0:
y = float(tftAbsDelta [1] - coords [1] + tftEnd [1]) / float(tftAbsDelta [1]) * float(surfaceSize [1])
else:
y = float(coords [1] - tftOrig [1]) / float(tftAbsDelta [1]) * float(surfaceSize [1])
return (int(x), int(y))
# Was useful to see what pieces I would need from the evdev events
def printEvent(event):
print(evdev.categorize(event))
print("Value: {0}".format(event.value))
print("Type: {0}".format(event.type))
print("Code: {0}".format(event.code))
while True:
r,w,x = select.select([touch], [], [])
for event in touch.read():
if event.type == evdev.ecodes.EV_ABS:
if event.code == 1:
X = event.value
elif event.code == 0:
Y = event.value
elif event.type == evdev.ecodes.EV_KEY:
if event.code == 330 and event.value == 1:
printEvent(event)
p = getPixelsFromCoordinates((X, Y))
if 12 <= p[0] <= 72 and 210 <= p[1] <= 230:
num = 0
if 92 <= p[0] <= 154 and 210 <= p[1] <= 230:
num = 1
if 173 <= p[0] <= 234 and 210 <= p[1] <= 230:
num = 2
if 255 <= p[0] <= 317 and 210 <= p[1] <= 230:
num = 3
if 290 <= p[0] <= 320 and 0 <= p[1] <= 30:
pygame.quit()
quit()
print(num)
pygame.quit()
quit()

Answer 1

Solved!
With the comments from #sloth and #Kingsley I rewrote the code to:
r,w,x = select.select([touch], [], [], 0)
if ( touch in r ):
for event in touch.read():
if event.type == evdev.ecodes.EV_ABS:
if event.code == 1:
X = event.value
elif event.code == 0:
Y = event.value
elif event.type == evdev.ecodes.EV_KEY:
if event.code == 330 and event.value == 1:
printEvent(event)
Now the loop runs even if there is no input, and input is working ok also.