Running xinput to change touchpad settings

Question

I am looking for some feedback on the code below, mainly for efficiency or mechanism correctness (like eval vs. subprocess). I am also curious if .find() is the best mechanism to use here. I am not familiar with regex, so my crutch (or benefit, depending) is using .find() over learning a sublanguage like regex.

import subprocess
get_device_id = subprocess.Popen(["xinput", "list", "SynPS/2 Synaptics TouchPad"], stdout=subprocess.PIPE)
gdi_str = str(get_device_id.stdout.read())
gdi_id_find = (gdi_str[gdi_str.find('id='):])
gdi_len = 3
gdi = (gdi_id_find[gdi_len:5])
if gdi.isdigit():
 device_id = gdi
else:
 pass
get_prop_id = subprocess.Popen(["xinput", "list-props", "15"], stdout=subprocess.PIPE)
r = str(get_prop_id.stdout.read())
if "2 Synaptics TouchPad" in r:
 b = (r[r.find('libinput Tapping Enabled ('):])
 bLen = len('libinput Tapping Enabled (')
 b = (b[bLen:b.find(')')])
 if b.isdigit():
 prop_id = b
 else:
 pass
subprocess.run(["xinput", "set-prop", device_id, prop_id, "1"])

This code parses the output of:

xinput list SynPS/2 Synaptics TouchPad

to get a numerical device ID, in this case 15:

SynPS/2 Synaptics TouchPad id=15 [slave pointer (2)]

The code then runs:

xinput list-props 15 # 15 is our parsed id

and parses this output:

Device 'SynPS/2 Synaptics TouchPad':
Device Enabled (147): 1
Coordinate Transformation Matrix (149): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
libinput Tapping Enabled (300): 0
libinput Tapping Enabled Default (301): 0
libinput Tapping Drag Enabled (302): 1
libinput Tapping Drag Enabled Default (303): 1
libinput Tapping Drag Lock Enabled (304): 0
libinput Tapping Drag Lock Enabled Default (305): 0
libinput Tapping Button Mapping Enabled (306): 1, 0
libinput Tapping Button Mapping Default (307): 1, 0
libinput Natural Scrolling Enabled (282): 0
libinput Natural Scrolling Enabled Default (283): 0
libinput Disable While Typing Enabled (308): 1
libinput Disable While Typing Enabled Default (309): 1
libinput Scroll Methods Available (286): 1, 1, 0
libinput Scroll Method Enabled (287): 1, 0, 0
libinput Scroll Method Enabled Default (288): 1, 0, 0
libinput Click Methods Available (310): 1, 1
libinput Click Method Enabled (311): 1, 0
libinput Click Method Enabled Default (312): 1, 0
libinput Middle Emulation Enabled (291): 0
libinput Middle Emulation Enabled Default (292): 0
libinput Accel Speed (293): 0.000000
libinput Accel Speed Default (294): 0.000000
libinput Left Handed Enabled (298): 0
libinput Left Handed Enabled Default (299): 0
libinput Send Events Modes Available (267): 1, 1
libinput Send Events Mode Enabled (268): 0, 0
libinput Send Events Mode Enabled Default (269): 0, 0
Device Node (270): "/dev/input/event10"
Device Product ID (271): 2, 7
libinput Drag Lock Buttons (284): <no items>
libinput Horizontal Scroll Enabled (285): 1

for the purposes of getting the prop-id for "libinput Tapping Enabled", in this case 300:

libinput Tapping Enabled (300): 0

Once the value is established, the code does a basic check for .isdigit() and if True, presents the values to:

subprocess.run(["xinput", "set-prop", device_id, prop_id, "1"])

Which ultimately sets the value to 1:

libinput Tapping Enabled (300): 1

Answer 1

There's no need for a redundant pass after your if; these can be deleted:

else:
 pass

---

xinput --list and xinput --list-props aren't long-running commands. It's simpler to subprocess.run() them, with standard output redirected to a variable:

get_device_id = subprocess.run(["xinput", "list",
 "SynPS/2 Synaptics TouchPad"],
 capture_output=True)
if get_device_id.returncode != 0
 sys.exit(get_device_id.returncode)
gdi_str = get_device_id.stdout

---

I don't believe that first command is actually required - xinput --list-props is quite happy to accept a device name instead of a property:

xinput --list-props 'SynPS/2 Synaptics TouchPad'