Difference between calling a python script by terminal and by PHP? Where is the Error?

I have a PHP script, that calls a python script by

$call_python = "python ../python/lp_3.py ".$author;
$python_output = Null;
$mystring = exec($call_python, $output_python);

This produces me an error in the log:

$ vi logs/error_log shows
....
Traceback (most recent call last):
    File "../python/lp_3.py", line 14, in <module>
        import MySQLdb
ImportError: No module named MySQLdb

If I do python python/lp_3.py in the terminal everything is fine. What do I miss?

Edit:

After the suggestion of @S.Lott I had a look at the variables PA开发者_运维知识库TH and PYTHONPATH both in the terminal and in PHP.

In the terminal:

$ echo $PYTHONPATH

$ echo $PATH
/opt/local/bin:/opt/local/sbin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/local/git/bin:/usr/texbin:/usr/X11/bin

As you can see, PYTHONPATH is empty.

In PHP:

echo getenv("PYTHONPATH"); // NOTHING
echo getenv("PATH"); // /usr/bin:/bin:/usr/sbin:/sbin

Perhaps I should mention that the first two lines in my python script are

#!/usr/bin/env python
# encoding: utf-8

I am open for suggestions. =)

Edit2:

I checked every installed python version on my mac. I found out, that python2.7 has no MySQLdb installed. Is there a way to tell PHP not to use python2.7 and to use e.g. python2.6 instead? I tryed toying with setenv() in PHP but I couldn't figure out how to use it properly, and I don't even know if this is the right approach.

---

In your PHP code, you're just calling "python", and letting PHP decide which version of Python to use. Use an explicit path to a specific Python binary, (e.g. /usr/bin/python2.6).

You need to know the exact path to the version of Python that has MySQLdb installed.

---

$call_python = "/opt/local/bin/python2.6 ../python/lp_3.py ".$author;
$python_output = Null;
$mystring = exec($call_python, $output_python);

did the job. Like @AJ pointed out, I had to tell python which version to chose. I chose a version where MySQLdb was available and all was fine.