`crontab` fails to run Python3 code at boot (no GUI involved)

Question

After searching for some time- I can;t find the reason that my python3 code won't execute during boot. I'm using Rpi Zero, using StrechLite OS. Code run OK when is executed from command line.

crontab contains:

@reboot /usr/bin/pigpiod
@reboot /usr/bin/python3 /home/guy/Documents/github/Rpi/SmartHome/tst.py & 

try 1:

I've created a bash file (containing echo "guy" >>log.log )to see if cron job is running OK- and redirected its output to a text file. All went well.

try 2:

bash file was edited to run ( python3 /home/guy/Documents/github/Rpi/SmartHome/tst.py ) , but it failed.

try 3:

a simple python code was written, 123.py containing a single line: print("GUY") to be executed as : @reboot /usr/bin/python3 /home/guy/Documents/github/Rpi/SmartHome/123.py >>log.txt in order to check if something is python code during boot time, make it fail- but still python code is not executed during boot.

What is done wrong in order to run a python script this way?

• Brick: What's in your python script? That might be failing due to path issues.
• Jaromanda X: crontab outputs information to /var/log/cron.log - anything there to indicate what the failure is?
• joan: The pigpio daemon needs to be run as root. Best to put the first line in the root crontab. Also the daemon may take a second or so to launch. Perhaps you need a delay before launching your script if it is using pigpio.
• guyd: @Brick path was checked and is correct
• guyd: @joan pig poof is running ok. The problem is execution of second line

Answer 1

After trying solving it with creation of daemon service (systemctl), which yield same unwanted result - I found the reason why:

using in crontab or daemon service - couldn't get $PYTHONPATH in time ( or boot sequence ) to find path needed to run a certain module I use.

so I added to my python code: sys.path.append('/home/guy/Documents/github/Rpi/GPIO_Projects/lcd') -in oder to find that particular module handling LCD display.

BTW- the above path is part of $PYTHONPATH, which probaby update after logging in, or running python IDE, but not when trying to automatically execute a code after OS boots up ( without logging in ).

Guy