Possible import error for pandas and matplotlib when calling Python3 via PHP shell_exec

I am experiencing a strange behaviour when trying to execute two different Python 3 scripts via PHP shell_exec() function. The first Python script is called the following way in PHP:

$jsondatash = escapeshellarg($jsondata);
// Execute the python script with the JSON data
$resultpy = shell_exec("/usr/bin/python3 /var/www/testsite/py/script1.py 2>&1 $jsondatash");

I escape some json data ($jsondatash) and run a Python function (script1.py) on this data via shell_exec(). The result of the Python workflow is stored in the PHP array $resultpy. The Python test script looks like this:

from collections import OrderedDict
import sys, json
import scipy
import scipy.cluster.hierarchy as sch
import pandas as pd
import matplotlib


# Load the data that PHP sent
try:
     data = json.loads(sys.argv[1], object_pairs_hook=OrderedDict) 

except (ValueError, TypeError, IndexError, KeyError) as e:
     print (json.dumps({'error': str(e)}))
     sys.exit(1)

print (json.dumps(data))

It is just reading the data and sending it back to PHP via shell. As a result, however, I get an empty object back, indicating that the Python 3 code cannot be executed. This is the Apache2 error.log:

PHP Fatal error: Uncaught TypeError: array_keys(): Argument #1 ($array) must be of type array, null given 

No Python-specific error information, only the error for the empty array in PHP. When I comment out both pandas and matplotlib from the Python test script

from collections import OrderedDict
import sys, json
import scipy
import scipy.cluster.hierarchy as sch
#import pandas as pd
#import matplotlib


# Load the data that PHP sent
try:
     data = json.loads(sys.argv[1], object_pairs_hook=OrderedDict) 

except (ValueError, TypeError, IndexError, KeyError) as e:
     print (json.dumps({'error': str(e)}))
     sys.exit(1)

print (json.dumps(data))

, I can successfully run the script via shell_exec(). So there must be some sort of loading error for both Python 3 libraries when executing the Python script via PHP.

The same behaviour I am experiencing when writing the json data in PHP to a file (inputfile.json), reading the file in Python, writing the data in Python to another file (outputfile.json), and reading this file back into PHP. This is the PHP code:

$jsondata = fopen('/var/www/testsite/files/inputfile.json', 'w');
fwrite($jsondata, $data);
fclose($jsondata);    

shell_exec("/usr/bin/python3 /var/www/testsite/py/script2.py 2>&1");
$resultpy = file_get_contents('/var/www/testsite/files/outputfile.json');

This is the corresponding script2.py Python code:

from collections import OrderedDict
import sys, json
import scipy
import scipy.cluster.hierarchy as sch
import pandas as pd
import matplotlib

# Load the data from json file
try:
   with open('/var/www/testsite/files/inputfile.json', 'r') as inputfile:
   data = json.load(inputfile, object_pairs_hook=OrderedDict) 
except (ValueError, TypeError, IndexError, KeyError) as e:
   print (json.dumps({'error': str(e)}))
   sys.exit(1)

# write data to json outputfile
with open('/var/www/testsite/files/outputfile.json', 'w') as outputfile:
json.dump(data, outputfile)

When executing the Python code directly in shell

/usr/bin/python3 /var/www/testsite/py/script2.py 2>&1

, I get the exspected output, but when executing the Python code in PHP using shell_exec(), the output file outputfile.json is empty. Again, if I remove both pandas and matplotlib from the Python script, it also runs successfully via PHP shell_exec().

These tests show the following: (1) Both Python scripts can be executed via PHP shell_exec(), but only if I remove loading pandas and matplotlib from the Python scripts. (2) Loading pandas and matplotlib is not a problem per se, since I can execute the Python script2.py including both libraries directly in shell and get the exspected output.

Why can I run the excact same python code on Apache2 directly in shell, but not via shell_exec() in PHP? From my test, it looks like it has to do with both pandas and matplotlib failing to load and terminating the python scripts.

Edit: Python3 version is 3.8.10, PHP version is 8.2.8, and this is the output after installing pandas and matplotlib:

pip install pandas
> Successfully installed pandas-2.0.3 python-dateutil-2.8.2 pytz-2023.3 tzdata-2023.3
pip install matplotlib
> Successfully installed contourpy-1.1.0 cycler-0.11.0 fonttools-4.40.0 importlib-resources-6.0.0
> kiwisolver-1.4.4 matplotlib-3.7.2 packaging-23.1 pillow-10.0.0 pyparsing-3.0.9 zipp-3.15.0

Edit2: I was wondering if scipy, which can be loaded and pandas, which fails to load, are located in the same path, and indeed they are:

Name: scipy
Version: 1.10.1
Location: /home/ubuntu/.local/lib/python3.8/site-packages

Name: pandas
Version: 1.5.3
Location: /home/ubuntu/.local/lib/python3.8/site-packages

I tested an older version of pandas (v.1.5.3 - see above), and have now installed the current version v.2.0.3. Both terminate the python script when imported. All additional packages required by pandas are installed.

Name: pandas
Version: 2.0.3
Location: /home/ubuntu/.local/lib/python3.8/site-packages

Python 3 sys.path is:

['', '/usr/lib/python38.zip', '/usr/lib/python3.8', '/usr/lib/python3.8/lib-dynload', '/home/ubuntu/.local/lib/python3.8/site-packages', '/usr/local/lib/python3.8/dist-packages', '/usr/lib/python3/dist-packages']

Edit3: I found that the following method (https://stackoverflow.com/a/44128762/8008652) allows me to retrieve the Python 3 error in PHP and print it in the html output:

exec('/usr/bin/python3 /var/www/testsite/py/script2.py 2>&1', $output, $return_var);
  if ($return_var>0) {
    var_dump($output);
  }

This is the Python 3 error:

 array(14) { [0]=> string(34) "Traceback (most recent call last):" [1]=> string(77) " File "/var/www/testsite/py/script2.py", line 6, in " [2]=> string(23) " import pandas as pd" [3]=> string(80) " File "/usr/lib/python3/dist-packages/pandas/__init__.py", line 55, in " [4]=> string(33) " from pandas.core.api import (" [5]=> string(79) " File "/usr/lib/python3/dist-packages/pandas/core/api.py", line 5, in " [6]=> string(44) " from pandas.core.arrays.integer import (" [7]=> string(92) " File "/usr/lib/python3/dist-packages/pandas/core/arrays/__init__.py", line 10, in " [8]=> string(53) " from .interval import IntervalArray # noqa: F401" [9]=> string(92) " File "/usr/lib/python3/dist-packages/pandas/core/arrays/interval.py", line 38, in " [10]=> string(60) " from pandas.core.indexes.base import Index, ensure_index" [11]=> string(89) " File "/usr/lib/python3/dist-packages/pandas/core/indexes/base.py", line 74, in " [12]=> string(49) " from pandas.core.strings import StringMethods" [13]=> string(139) "ImportError: cannot import name 'StringMethods' from 'pandas.core.strings' (/usr/lib/python3/dist-packages/pandas/core/strings/__init__.py)" } 

As I suspected from my previous tests, it's an import error related to the pandas library (ImportError: cannot import name 'StringMethods' from 'pandas.core.strings).