You may start out with the NLTK Book, which is one of the most widely used introductions for Python NLTK so here's some steps that will save you some trouble (installing required modules and so on) and some hours' worth of googling for answers:
We're using Python 2.7 on Ubuntu
$ sudo apt-get install python-pip $ sudo apt-get install python-setuptools
(For numeric operations)
$ pip install numpy
(For plotting graphs)
$ sudo apt-get install libfreetype6-dev $ sudo apt-get install python-tk $ pip install matplotlib
(The library itself)
$ pip install nltk
pipdoes not, by default, install missing system dependencies (i.e. ubuntu packages) if they're needed for a python package.
For example, if
pip install scipyfails, try doing
apt-get install python-scipyinstead.