cartouche is available on the Python Package Index (PyPI) and can be installed with easy_install so long as you have setuptools installed already:
$ easy_install cartouche
Alternatively, you can download and unpack the source distribution from the cartouche downloads page or PyPI. You should then unpack the source distribution into a temporary directory and run the setup script which will install cartouche into the current Python environment, for example:
$ tar xzf cartouche-1.0.tar.gz
$ cd cartouche-1.0
$ python setup.py install