python packages

Installing Python packages

The EPD distribution of Python comes with many of the Python packages we'll use over the course of the semester. However, eventually you'll come across a new package that isn't included in EPD that you'll want to take advantage of. There are a variety of ways to install packages but in recent years package managers have become the tool of choice. A well designed package manager will download the package of interest plus any dependencies from a central repository (PyPI -- the Python Package Index), carry out any build instructions, and install the resulting code in the appropriate directories.

For years the most commonly used package manager among Python users was a tool called easy_install. You already have access to easy_install as part of the EPD. You'll still see many references to using easy_install so you should be aware of it. However, recently a new package manager called Pip has become popular in the Python community. Pip offers some additional checks to prevent things like partially-completed installations, and offers the ability to easily uninstall packages as well. We'll take a look at installing Pip and using it to install a literate programming package called Pweave.

Downloading and installing Pip

The Pip installer can be downloaded from get-pip.py. Note: if downloaded this via a web-browser use Right click > Save Link As.

If you have access to the curl command line utility (available by default on OSX, available in the Cygwin package manager) then you can download get-pip.py as so:

$ curl -O https://raw.github.com/pypa/pip/master/contrib/get-pip.py

Once you've downloaded get-pip.py you can install it

$ sudo python get-pip.py # sudo NOT needed on cygwin

You'll get a variety of output, but the key line you want to see is Successfully installed pip. You can type which pip to confirm that pip has been installed correctly.

Using Pip

Now that Pip is installed, let's take it for a quick test spin to check out some of it's features. Let's start by looking at the help:

$ pip help | less  # use more as the pager on windows
Usage: pip COMMAND [OPTIONS]
    ... lots of output truncated ...

Commands available:
  bundle: Create pybundles (archives containing multiple packages)
  freeze: Output all currently installed packages (exact versions) to stdout
  help: Show available commands
  install: Install packages
  search: Search PyPI
  uninstall: Uninstall packages
  unzip: Unzip individual packages
  zip: Zip individual packages

Let's use the 'search' command to search for the Pweave package.

$ pip search "Pweave"
Pweave                    - Literate programming with reST or LaTeX in Sweave
                            style

Great, the package we want is available from PyPI. Now let's install it:

$ sudo pip install Pweave

After a successful installation we can check that Pweave is now available to us:

$ which Pweave

That's all there is to it. See the Pip docs for more info.