How to pragmatically check for a GPIO warning? - Raspberry Pi Forums

so have python script works great @ blinking led. if run second instance of script following expected warning:
runtimewarning: channel in use, continuing anyway. use gpio.setwarnings(false) disable warnings.

have situation call program more once sometimes, never want more 1 instance run. want catch error in python code , exit instance of program, because means have instance running.

if there no way catch particular gpio runtime warning, current idiomatic way force python run 1 instance of script @ time?

help!

i don't know python, ways of checking there 1 instance of script running include:

1) create pidfile (usually in /run or /var/run same place) called scriptname.pid containing pid of script. when script starts should check presence of such file, read pid , see if pid still executing. if so, exit.

2) create lockfile. open file writing, in tmpfs (like /run again), call scriptname.lock. don't need write though. when script starts should try opening file write access, if fails file in use , copy of script running.

3) use "pidof" command check if same name running.

4) parse output "ps" command see if same name running.

there other ways too.

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