PHP not executing python script correctly

Question

I'm executing a python script from a php page like so: exec("python ./test.py");

This script runs fine if I don't open a serial port in it. If I do, however, (and this is the whole point of calling the python script in the first place), the script doesn't execute properly.

If I call a simple python script that prints a statement -

print "This works!"

Then I get the desired output in my php page. But, if I open a serial port, I no longer get the output of "This works!", and the serial data is not getting sent to the receiving device -

import serial
ser = serial.Serial("/dev/ttyACM0",9600)
print "This works!"

Both scripts run fine from the command line.

Is this a php limitation? I have tried other methods of execution such as popen and system, but they didn't work for me either.

Running from the command line is done with YOUR permissions. Running it under Apache is doine with Apache's permissions. Check that apache can open ttyACM0. — Marc B
– Marc B, Commented Jul 11, 2012 at 2:52
run python -c'import sys; print >>sys.stderr, "stderr is visible"' — jfs
– jfs, Commented Jul 11, 2012 at 3:06

Ned Batchelder · Accepted Answer · 2012-07-11 02:52:55Z

2

Perhaps you aren't getting complete error reporting from your Python execution. Try adding raise Exception('Boo!') as the first line of you Python program to find out if you are or not. If you don't get the exception and a traceback, then your program is probably failing on the serial.Serial line, but you aren't hearing about it.

answered Jul 11, 2012 at 2:52

Ned Batchelder

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4 Comments

penguinrob Over a year ago

I get the exception when I run from command line, but nothing when run from php. Edit: That is with the exception before anything else.

penguinrob Over a year ago

If I add a print statement before the exception, I get the output of it. But it still doesn't output the exception

Ned Batchelder Over a year ago

It sounds like you are getting stdout but not stderr. Either fix your process spawning so you do get stderr, or wrap your entire Python program so that error handling goes to stdout.

penguinrob Over a year ago

Alright, sent stderr to stdout and am now getting all the error messages.

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