What is the difference between running a script from the command line and from exec() with PHP?

Question

I'm trying to run a Python script using exec() from within PHP. My command works fine when I run it directly using a cmd window, but it produces an error when I run it from exec() in PHP.

My Python script uses NTLK to find proper nouns. Example command:

"C:\Python25\python.exe" "C:\wamp\projects\python\trunk\tests\find_proper_nouns.py" "I went to London this morning" 

returns [London] when I run it from cmd, but throws an error in the Apache log when I run the same command from exec().The script is defintely getting run OK - if I change the python script to be print "Hello World" that is returned fine.

I know it's a big ask for anyone to know how to fix this NLTK error, but I could really do with any pointers as to why running it from exec is different to cmd. (The command is identical).

I'm running WAMP on Windows 7 with Apache 2.2.11.

Here's the error in the Apache log:

Traceback (most recent call last):
  File "C:\wamp\projects\python\trunk\tests\find_proper_nouns_command_line.py", line 6, in <module>
    parts = nltk.pos_tag(text)
  File "C:\Python25\lib\site-packages\nltk\tag\__init__.py", line 62, in pos_tag
    tagger = nltk.data.load(_POS_TAGGER)
  File "C:\Python25\lib\site-packages\nltk\data.py", line 590, in load
    resource_val = pickle.load(_open(resource_url))
  File "C:\Python25\lib\site-packages\nltk\data.py", line 669, in _open
    return find(path).open()
  File "C:\Python25\lib\site-packages\nltk\data.py", line 451, in find
    raise LookupError(resource_not_found)
LookupError: 
**********************************************************************
  Resource 'taggers/maxent_treebank_pos_tagger/english.pickle' not
  found.  Please use the NLTK Downloader to obtain the resource:
  >>> nltk.download().
  Searched in:
    - 'C:\\nltk_data'
    - 'D:\\nltk_data'
    - 'E:\\nltk_data'
    - 'C:\\Python25\\nltk_data'
    - 'C:\\Python25\\lib\\nltk_data'
    - 'C:\\Windows\\system32\\config\\systemprofile\\AppData\\Roaming\\nltk_data'
**********************************************************************

Answer 1

Your web server likely runs with other privileges than yourself. Possible problems include:

• Path/file permission: can the web server user access the files it needs?
• Different environment: are all necessary environment variables (PATH, Python-specific stuff, …) set?
• Configuration: are there per-user configurations for Python or the module?

Tip: execute set in both the command prompt and from the PHP process and check the differences.