:orphan: This article should not be added to a toctree for now

.. _install3-osx:

Installing Python 3 on Mac OS X
================================

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

You do not need to install or configure anything else to use Python 2. These
instructions document the installation of Python 3.

The version of Python that ships with OS X is great for learning, but it's not
good for development. The version shipped with OS X may be out of date from the
`official current Python release <https://www.python.org/downloads/mac-osx/>`_,
which is considered the stable production version.

Doing it Right
--------------

Let's install a real version of Python.

Before installing Python, you'll need to install GCC. GCC can be obtained
by downloading `XCode <http://developer.apple.com/xcode/>`_, the smaller
`Command Line Tools <https://developer.apple.com/downloads/>`_ (must have an
Apple account) or the even smaller `OSX-GCC-Installer <https://github.com/kennethreitz/osx-gcc-installer#readme>`_
package.

.. note::
    If you already have XCode installed, do not install OSX-GCC-Installer.
    In combination, the software can cause issues that are difficult to
    diagnose.

.. note::
    If you perform a fresh install of XCode, you will also need to add the
    commandline tools by running ``xcode-select --install`` on the terminal.

While OS X comes with a large number of UNIX utilities, those familiar with
Linux systems will notice one key component missing: a package manager.
`Homebrew <http://brew.sh>`_ fills this void.

To `install Homebrew <http://brew.sh/#install>`_, open :file:`Terminal` or
your favorite OSX terminal emulator and run

.. code-block:: console

    $ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

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 :envvar:`PATH` environment variable. You can do this by adding the following
line at the bottom of your :file:`~/.profile` file

.. code-block:: console

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

Now, we can install Python 3:

.. code-block:: console

    $ brew install python3

This will take a minute or two.


Pip
---

Homebrew installs ``pip3`` for you.

``pip3`` is the alias for the Python 3 version of ``pip`` on systems with both
the Homebrew'd Python 2 and 3 installed.

Working with Python 3
---------------------

At this point, you have the system Python 2.7 available, potentially the
:ref:`Homebrew version of Python 2 <install-osx>` installed, and the Homebrew
version of Python 3 as well.

.. code-block:: console

    $ python

will launch the Python 2 interpreter.

.. code-block:: console

    $ python3

will launch the Python 3 interpreter.

``pip3`` and ``pip`` will both be available.  If the Homebrew version of Python
2 is not installed, they will be the same.  If the Homebrew version of Python 2
is installed then ``pip`` will point to Python 2 and ``pip3`` will point to
Python 3.


Virtual Environments
--------------------

A Virtual Environment (commonly referred to as a 'virtualenv') is a tool to keep
the dependencies required by different projects in separate places, by creating
virtual Python environments for them. It solves the "Project X depends on
version 1.x but, Project Y needs 4.x" dilemma, and keeps your global
site-packages directory clean and manageable.

For example, you can work on a project which requires Django 1.10 while also
maintaining a project which requires Django 1.8.

To start using this and see more information: :ref:`Virtual Environments <virtualenvironments-ref>` docs.

--------------------------------

This page is a remixed version of `another guide <http://www.stuartellis.eu/articles/python-development-windows/>`_,
which is available under the same license.