How to execute Python script in PHP

How do I execute Python script in PHP?
You want to SSH to the remote server via PHP, then execute a python file on the server, get the results, and print from PHP.
My code is as follows:

$connection = Ssh2_connect (' remote-server ', 22);
Ssh2_auth_password ($connection, ' root ', ' pwd ');

$string = ssh2_exec ($connection, ' Python pythonfile.py; sleep 20 ');
Stream_set_blocking ($string, true);
echo stream_get_contents ($string);

But the null value is printed in PHP.
If I put
$string = ssh2_exec ($connection, ' Python pythonfile.py; sleep 20 ')
Replaced by
$string = ssh2_exec ($connection, ' ls-l ')
There is no problem, the program output normally.

The python file on the remote server typically takes 15 seconds to run, so I set sleep 20, but I still get no results.
Want to ask if the code is wrong? How to correct it? PHP Python SSH2

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------Solution--------------------
References:

solved, I changed the code again.
$stream = ssh2_exec ($connection, ' CD dca_automation/main/qautilities/utils; python cluster_discovery.py ');
Stream_set_blocking ($stream, true);

$string = Stream_get_contents ($stream);
Echo $string;

No longer output Python results to a file, let $stream get it directly, because "in non-blocking mode a fgets () call would always return right away while in blocking mode It will wait for data to become available on the stream ", so, if the previous code, once the Output.txt file generation, even if the results have not been written up, $stream have obtained data, so Strea M_set_blocking () will automatically terminate. But if I write the result of the python directly onto the stream, the result is not fully generated before the process will block.
I don't know what I'm explaining, right? The inappropriate place welcomes everyone to correct me.

No mistake, it is the stream that receives the data returned by the shell, triggering the stream to return the result, thus executing the stream_get_contents

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