The latest version of Mac OS X, Mountain Lion, comes with Python 2.7 out of the box.

You do not need to install or configure anything else to use Python. Having said that, I would strongly recommend that you install the tools and libraries described in the next section before you start building Python applications for real-world use. In particular, you should always install Distribute, as it makes it much easier for you to use other third-party Python libraries.

The version of Python that ships with OS X is great for learning, but it's not good for development. It's slightly out of date, and Apple has made significant changes that can cause hidden bugs.

Let's install a real version of Python.

Before installing Python, you'll need to install GCC. GCC can be obtained by downloading XCode, the smaller Command Line Tools (must have an Apple account) or the even smaller OSX-GCC-Installer package.

While Lion comes with a large number of UNIX utilities, those familiar with Linux systems will notice one key component missing: a decent package manager. Homebrew fills this void.

To install Homebrew, simply run

$ ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"

The script will explain what changes it will make and prompt you before the installation begins. Once you've installed Homebrew, insert the Homebrew directory at the top of your PATH environment variable. You can do this by adding the following line at the bottom of your ~/.bashrc file

export PATH=/usr/local/bin:$PATH

Now, we can install Python 2.7:

$ brew install python

This will take a minute or two. Once that's complete, you'll have to add the new Python scripts directory to your PATH

export PATH=/usr/local/share/python:$PATH

The most crucial third-party Python software of all is Distribute, which extends the packaging and installation facilities provided by the distutils in the standard library. Once you add Distribute to your Python system you can download and install any compliant Python software product with a single command. It also enables you to add this network installation capability to your own Python software with very little work. Homebrew already installed Distribute for you.

Happily, when you ran brew install python, Homebrew also installed pip. Pip allows for uninstallation of packages, and is actively maintained.

After Distribute & Pip, the next development tool that you should install is virtualenv. Use pip

$ pip install virtualenv

The virtualenv kit provides the ability to create virtual Python environments that do not interfere with either each other, or the main Python installation. If you install virtualenv before you begin coding then you can get into the habit of using it to create completely clean Python environments for each project. This is particularly important for Web development, where each framework and application will have many dependencies.

To set up a new Python environment, change the working directory to where ever you want to store the environment, and run the virtualenv utility in your project's directory

$ virtualenv --distribute venv

To use an environment, run source venv/bin/activate. Your command prompt will change to show the active environment. Once you have finished working in the current virtual environment, run deactivate to restore your settings to normal.

Each new environment automatically includes a copy of pip, so that you can setup the third-party libraries and tools that you want to use in that environment. Put your own code within a subdirectory of the environment, however you wish. When you no longer need a particular environment, simply copy your code out of it, and then delete the main directory for the environment.

An useful set of extensions to virtualenv is available in virtualenvwrapper, RTFD to find out more.

This page is a remixed version of another guide, which is available under the same license.