Ubuntu add directory to Python path

I want to run third part tool written in python on my ubuntu machine (corgy tool).

However I don't know how to add additional modules to Python path.

cat doc/download.rst There is currently no setup.py, so you need to manually add the download directory to your PYTHON_PATH environment variable. 

How can I add directory to PYTHON_PATH?

I have tried:
export PYTHON_PATH=/home/user/directory:$PYTHON_PATH && source .bashrc
export PATH=/home/user/directory:$PATH && source .bashrc

python
import sys
sys.path.append("/home/user/directory/")

But when I try to run this tool I get:

Traceback (most recent call last): File "examples/dotbracket_to_bulge_graph.py", line 4, in <module> import corgy.graph.bulge_graph as cgb ImportError: No module named corgy.graph.bulge_graph 

2 Answers

Create a .bash_profile in your home directory. Then, add the line

PYTHONPATH=$PYTHONPATH:new_dir EXPORT $PYTHONPATH 

Or even better:

if [ -d "new_dir" ] ; then PYTHONPATH="$PYTHONPATH:new_dir" fi EXPORT $PYTHONPATH 

The .bash_profile properties are loaded every time you log in.

The source command is useful if you don't want to log in again.

@fedorqui's answer above was almost good for me, but there is at least one mistake (I am not sure about the export statement in all caps, I am a complete newbie). There should not be a $ sign preceding PYTHONPATH in the export statement. So the options would be:

Create a .bash_profile in your home directory. Then, add the line

PYTHONPATH=$PYTHONPATH:new_dir export PYTHONPATH 

Or even better:

if [ -d "new_dir" ] ; then PYTHONPATH="$PYTHONPATH:new_dir" fi export PYTHONPATH