4. Using Python on a Mac
************************

Author:
   Bob Savage <bobsavage@mac.com>

Python on a Mac running macOS is in principle very similar to Python
on any other Unix platform, but there are a number of additional
features such as the IDE and the Package Manager that are worth
pointing out.


4.1. Getting and Installing MacPython
=====================================

macOS since version 10.8 comes with Python 2.7 pre-installed by Apple.
If you wish, you are invited to install the most recent version of
Python 3 from the Python website (https://www.python.org).  A current
"universal binary" build of Python, which runs natively on the Mac's
new Intel and legacy PPC CPU's, is available there.

What you get after installing is a number of things:

* A "Python 3.9" folder in your "Applications" folder. In here you
  find IDLE, the development environment that is a standard part of
  official Python distributions; and PythonLauncher, which handles
  double-clicking Python scripts from the Finder.

* A framework "/Library/Frameworks/Python.framework", which includes
  the Python executable and libraries. The installer adds this
  location to your shell path. To uninstall MacPython, you can simply
  remove these three things. A symlink to the Python executable is
  placed in /usr/local/bin/.

The Apple-provided build of Python is installed in
"/System/Library/Frameworks/Python.framework" and "/usr/bin/python",
respectively. You should never modify or delete these, as they are
Apple-controlled and are used by Apple- or third-party software.
Remember that if you choose to install a newer Python version from
python.org, you will have two different but functional Python
installations on your computer, so it will be important that your
paths and usages are consistent with what you want to do.

IDLE includes a help menu that allows you to access Python
documentation. If you are completely new to Python you should start
reading the tutorial introduction in that document.

If you are familiar with Python on other Unix platforms you should
read the section on running Python scripts from the Unix shell.


4.1.1. How to run a Python script
---------------------------------

Your best way to get started with Python on macOS is through the IDLE
integrated development environment, see section The IDE and use the
Help menu when the IDE is running.

If you want to run Python scripts from the Terminal window command
line or from the Finder you first need an editor to create your
script. macOS comes with a number of standard Unix command line
editors, **vim** and **emacs** among them. If you want a more Mac-like
editor, **BBEdit** or **TextWrangler** from Bare Bones Software (see
http://www.barebones.com/products/bbedit/index.html) are good choices,
as is **TextMate** (see https://macromates.com/). Other editors
include **Gvim** (http://macvim-dev.github.io/macvim/) and
**Aquamacs** (http://aquamacs.org/).

To run your script from the Terminal window you must make sure that
"/usr/local/bin" is in your shell search path.

To run your script from the Finder you have two options:

* Drag it to **PythonLauncher**

* Select **PythonLauncher** as the default application to open your
  script (or any .py script) through the finder Info window and
  double-click it. **PythonLauncher** has various preferences to
  control how your script is launched. Option-dragging allows you to
  change these for one invocation, or use its Preferences menu to
  change things globally.


4.1.2. Running scripts with a GUI
---------------------------------

With older versions of Python, there is one macOS quirk that you need
to be aware of: programs that talk to the Aqua window manager (in
other words, anything that has a GUI) need to be run in a special way.
Use **pythonw** instead of **python** to start such scripts.

With Python 3.9, you can use either **python** or **pythonw**.


4.1.3. Configuration
--------------------

Python on macOS honors all standard Unix environment variables such as
"PYTHONPATH", but setting these variables for programs started from
the Finder is non-standard as the Finder does not read your ".profile"
or ".cshrc" at startup. You need to create a file
"~/.MacOSX/environment.plist". See Apple's Technical Document QA1067
for details.

For more information on installation Python packages in MacPython, see
section Installing Additional Python Packages.


4.2. The IDE
============

MacPython ships with the standard IDLE development environment. A good
introduction to using IDLE can be found at
http://www.hashcollision.org/hkn/python/idle_intro/index.html.


4.3. Installing Additional Python Packages
==========================================

There are several methods to install additional Python packages:

* Packages can be installed via the standard Python distutils mode
  ("python setup.py install").

* Many packages can also be installed via the **setuptools** extension
  or **pip** wrapper, see https://pip.pypa.io/.


4.4. GUI Programming on the Mac
===============================

There are several options for building GUI applications on the Mac
with Python.

*PyObjC* is a Python binding to Apple's Objective-C/Cocoa framework,
which is the foundation of most modern Mac development. Information on
PyObjC is available from https://pypi.org/project/pyobjc/.

The standard Python GUI toolkit is "tkinter", based on the cross-
platform Tk toolkit (https://www.tcl.tk). An Aqua-native version of Tk
is bundled with OS X by Apple, and the latest version can be
downloaded and installed from https://www.activestate.com; it can also
be built from source.

*wxPython* is another popular cross-platform GUI toolkit that runs
natively on macOS. Packages and documentation are available from
https://www.wxpython.org.

*PyQt* is another popular cross-platform GUI toolkit that runs
natively on macOS. More information can be found at
https://riverbankcomputing.com/software/pyqt/intro.


4.5. Distributing Python Applications on the Mac
================================================

The standard tool for deploying standalone Python applications on the
Mac is **py2app**. More information on installing and using py2app can
be found at http://undefined.org/python/#py2app.


4.6. Other Resources
====================

The MacPython mailing list is an excellent support resource for Python
users and developers on the Mac:

https://www.python.org/community/sigs/current/pythonmac-sig/

Another useful resource is the MacPython wiki:

https://wiki.python.org/moin/MacPython
