Reading live output of a python program using php

Question

I am making a PHP web page that executes a python program and while the python program is running, it displays the output in real-time. After following this answer, this is the code that I am trying.

$cmd = 'python execs/reduction_code.py';
while(@ ob_end_flush());

$proc = popen($cmd, 'r');
echo '<pre class="box">';

while(!feof($proc)){
    echo fread($proc, 4096);
    @ flush();
}

echo '</pre>';
pclose($proc);

After I start executing the program reduction_code.py, in every 30 seconds, it displays few print statements (telling about status of the program). The program takes approx 25 minutes to completely execute. This works well when i run the python program using terminal.

However, when i run this using the above php code, it doesn't show any output at all. The file reduction_code.py is executable and apache has the permission to execute and read it.

Also, when i run a simple python program to ping an address by replacing the value in $cmd as $cmd = 'python execs/test.py'; , I get the expected real-time output of ping probes in my page.

test.py is:

from subprocess import call
call(["ping", "-c", "10", "localhost"])

I am new to PHP and I have no idea why after running reduction.py, the page displays no output at all.

EDIT 1 : When I use $proc = popen($cmd.' 2>&1', 'r'); instead of $proc = popen($cmd, 'r'); to access any error message returned by shell. I get this error message printed on my webpage(at the place where output was expected to appear).

Resource id #9/usr/lib/python2.7/site-packages/IPython/utils/path.py:296: UserWarning: IPython parent '/root' is not a writable location, using a temp directory." using a temp directory."%parent)

/usr/lib64/python2.7/site-packages/astropy/config/configuration.py:687: ConfigurationMissingWarning: Configuration defaults will be used due to OSError:13 on None warn(ConfigurationMissingWarning(msg))
Traceback (most recent call last):
  File "execs/reduction_code.py", line 8, in 
    import matplotlib.pyplot as plt
  File "/usr/lib64/python2.7/site-packages/matplotlib/pyplot.py", line 26, in 
    from matplotlib.figure import Figure, figaspect
  File "/usr/lib64/python2.7/site-packages/matplotlib/figure.py", line 24, in 
    import matplotlib.artist as martist
  File "/usr/lib64/python2.7/site-packages/matplotlib/artist.py", line 7, in 
    from transforms import Bbox, IdentityTransform, TransformedBbox, \
  File "/usr/lib64/python2.7/site-packages/matplotlib/transforms.py", line 35, in 
    from matplotlib._path import (affine_transform, count_bboxes_overlapping_bbox,
ImportError: /opt/lampp/lib/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by /usr/lib64/python2.7/site-packages/matplotlib/_path.so)

Zoe O'Connell · Accepted Answer · 2016-02-09 14:07:52Z

2

It sounds like you need to make Python's output unbuffered - this is on by default when running from the command line, but otherwise off. The easiest way of fixing this is to add the -u argument to the hashbang at the start of the script:

#!/usr/bin/python -u

answered Feb 9, 2016 at 14:07

Zoe O'Connell

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3 Comments

Nikhil Gupta Over a year ago

Tried it. Still no improvement.

Zoe O'Connell Over a year ago

How about changing the first line of the PHP code to $cmd = 'python -u execs/reduction_code.py'; ?

Nikhil Gupta Over a year ago

Nothing changes even then.

Community · Accepted Answer · 2017-05-23 11:45:10Z

I found answer to my question. As error reported in last line of the output :

ImportError: /opt/lampp/lib/libstdc++.so.6: version `GLIBCXX_3.4.9' not found (required by /usr/lib64/python2.7/site-packages/matplotlib/_path.so)

I found out here that the libraries that lampp is using are too old and does not define GLIBCXX_3.4.9. So, at first I renamed the /opt/lampp/lib/libstdc++.so.6 to /opt/lampp/lib/libstdc++.so.6.orig and then changed the LD_LIBRARY_PATH by changing the command from this :

$proc = popen($cmd.' 2>&1', 'r');

to this:

$proc = popen("LD_LIBRARY_PATH=/usr/lib/ ".$cmd.' 2>&1', 'r');

After I ran my program after this change, another report generated which said that

Runtime Error: could not open display

After doing some search, I found from here and here it was the problem of matplotlib library. I learned that matplotlib library uses X-using backend by default. And X-using backend has problems with few servers. So I followed the answer and inserted these two lines in my reduction_code.py program

import matplotlib
matplotlib.use('Agg')

And now, everything is working as expected. Thank you for support.

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