Send Parameter to a Python Script Running at Background From PHP

Question

I have a python script (analyze.py) which takes a filename as a parameter and analyzes it. When it is done with analysis, it waits for another file name. What I want to do is:

Send file name as a parameter from PHP to Python.
Run analyze.py in the background as a daemon with the filename that came from PHP.

I can post the parameter from PHP as a command line argument to Python but I cannot send parameter to python script that already runs at the background.

Any ideas?

Is there a reason you can't just re-launch the Python script for each filename? There are sometimes good answers to this (e.g., the process startup overhead on Windows can be a significant fraction of a second, and if each file only takes 20ms to process, using a separate process for each would be stupid), but if you don't have one, why not keep it simple? (And also open the door to parallelizing the processing, etc.) — abarnert
– abarnert, Commented Oct 20, 2014 at 18:58
I cant relaunch the process because it has some training stuff in it. After training it enters the analysis process. Training must be done when the python script starts running. — Asım Sinan Yüksel
– Asım Sinan Yüksel, Commented Oct 20, 2014 at 19:03

abarnert · Accepted Answer · 2014-10-20 19:04:21Z

1

The obvious answer here is to either:

Run analyze.py once per filename, instead of running it as a daemon.
Pass analyze.py a whole slew of filenames at startup, instead of passing them one at a time.

But there may be a reason neither obvious answer will work in your case. If so, then you need some form of inter-process communication. There are a few alternatives:

Use the Python script's standard input to pass it data, by writing to it from the (PHP) parent process. (I'm not sure how to do this from PHP, or even if it's possible, but it's pretty simple from Python, sh, and many other languages, so …)
Open a TCP socket, Unix socket, named pipe, anonymous pipe, etc., giving one end to the Python child and keeping the other in the PHP parent. (Note that the first one is really just a special case of this one—under the covers, standard input is basically just an anonymous pipe between the child and parent.)
Open a region of shared memory, or an mmap-ed file, or similar in both parent and child. This probably also requires sharing a semaphore that you can use to build a condition or event, so the child has some way to wait on the next input.
Use some higher-level API that wraps up one of the above—e.g., write the Python child as a simple HTTP service (or JSON-RPC or ZeroMQ or pretty much anything you can find good libraries for in both languages); have the PHP code start that service and make requests as a client.

answered Oct 20, 2014 at 19:04

abarnert

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2 Comments

Asım Sinan Yüksel Over a year ago

This is awesome. Thank you so much. I wrote my python script as a HTTP service using JSON-RPC. It works like a charm :)

abarnert Over a year ago

@AsımSinanYüksel: Well, that was quick. :) It's amazing how easy it's gotten to do the high-level solutions nowadays.

Asım Sinan Yüksel · Accepted Answer · 2014-10-20 20:04:37Z

0

Here is what I did.

PHP Part:

<?php

$param1 = "filename";

$command = "python analyze.py ";
$command .= " $param1";

$pid = popen( $command,"r");
 echo "<body><pre>";
while( !feof( $pid ) )
{
 echo fread($pid, 256);
 flush();
 ob_flush();
}
pclose($pid);

?>

Python Part:

1. I used [JSON-RPC]: https://github.com/gerold-penz/python-jsonrpc to
create a http service that wraps my python script (runs forever)
2. Created a http client that calls the method of http service.
3. Printed the results in json format.

Works like a charm.

answered Oct 20, 2014 at 20:04

Asım Sinan Yüksel

7510 bronze badges

1 Comment

abarnert Over a year ago

You should be able to embed a JSON-RPC/HTTP client directly in your PHP instead of writing it as a separate service… but if this works, and you were able to write it with no problems in half an hour, it's hard to argue with success. :)

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