pyheif affect output in php when running external python code in php

Question

I found a weird bug in python pyheif library. I am trying to run external python code in php function exec('python command', $output); I can get the python message in array with second argument $output from exec().

python code (test.py):

# -*- coding: utf-8 -*-
import sys
import os
import base64
from PIL import Image # pip3 install pillow
import pyheif  # pip3 install pyheif
import io
print("hello world!")

php code (test.php):

<?php
exec("python3 test.py", $output);
var_dump($output);

This is working well on command line but not on the web browser. But when I remove import hyheif line or move print('hello world') ahead of hyheif line, it works both cli and web browser. I get the result: hello world string.

I got no clue. Does hyheic library cause this problem on the web browser while it works fine on the command line?

I need to import hyheic library for converting heic to jpeg on the browser. My problem is I am not able to get the result on php from python code.

When I import hyheif library, I get the following result:

shell:/var/www/myfolder$ php test.php
array(1) {
  [0]=>
  string(12) "hello world!"
}

on my chrome browser:

array(0){}