python - Importing Libraries Issue - "ImportError: No Module named ____"

Question

I've looked through a lot of the other question/answers for this topic but no avail.

I downloaded numpy and nltk using pip, and based on the messages I know the install location is: Requirement already satisfied (use --upgrade to upgrade): nltk in /usr/local/lib/python2.7/site-packages, so it looks like it's installing in the directory for version 2.7.

When I run python I get Python 2.7.3 (v2.7.3:70274d53c1dd, Apr 9 2012, 20:52:43), so that's clearly also version 2.7.

However, when I try "import nltk" or "import numpy" in the Python console, I always get the ImportError: No module named nltk error. Any advice would be greatly appreciated!

Answer 1

Try changing the PYTHONPATHenvironment variable. If you are using BASH the below should work. Other Linux shells will be slightly different in how they assign environment variables.

export PYTHONPATH=$PYTHONPATH:/usr/local/lib/python2.7/site-packages

Answer 2

The problem is that /usr/local/lib/python2.7/site-packages is not in your default path list. In order to verify this, run the following commands:

import sys
for pth in sys.path:
    print pth

You will get a list of the directories searched for modules. As you probably will not have /usr/local/lib/python2.7/site-packages in the list, you have the following options:

1. Remove nltk and install it again in one of the directories paths (note, that e.g. on Debian, it may be /usr/local/lib/python2.7/dist-packages.

2. On each run, set PYTHONPATH variable: export PYTHONPATH=$PYTHONPATH:/usr/local/lib/python2.7/site-packages (you can put this command in the $HOME/.bashrc file).

3. Put a file local.pth in /usr/lib/python2.7/site-packages or /usr/lib/python2.7/dist-packages (depending on the output of the script above), which contains a single line:

   /usr/local/lib/python2.7/site-packages
   

   This will add this directory to your default path list permanently.

4. (This one is recommended only for some seldom-used non-standard packages installed in some strange location, which is probably not your case) In the beginning of your script (before import nltk) add the following code:

   import sys
   sys.path.append("/usr/local/lib/python2.7/site-packages")