If you are lazy, just perform
$ easy_install -U plac
which will install the module on your system (and possibly argparse too, if it is not already installed). Notice that Python 3 requires the easy_install version of the distribute project.
If you prefer to install the full distribution from source, including the documentation, download the tarball, unpack it and run
$ python setup.py install
in the main directory, possibly as superuser.
Run
$ python doc/test_plac.py
or
$ nosetests doc
or
$ py.test doc
Some tests will fail if sqlalchemy is not installed. Run an easy_install -U sqlalchemy
or just ignore them.
The source code and the documentation are hosted on Google code. Here is the full documentation in HTML and PDF form: