jessenoller.com

In a com­plete tan­gent from my numer­ous other projects, I’ve had a few peo­ple ask me recently about python on the mac, how to get started/etc.

I’m going to solely focus on python in Leop­ard (10.5.x) and not any­thing before that. Any­thing before that is dead to me! DEAD!

If you open a shiny new mac­book, and want to get started hack­ing, the first place you need to stop is the Apple Dev site, and down­load the lat­est ver­sion of XCode. XCode installs gcc and other tools which you are going to want and need sooner or later. It’s a mon­ster down­load, but bite the bullet.

By default, Leop­ard comes with Python 2.5.1 — the bina­ries and stan­dard library (and any Leop­ard addi­tions) are installed into /System/Library/Frameworks/Python.framework/Versions/2.5/ /Library/Python//, the site-packages direc­tory is in /Library/Python/…/site-packages. This is known as a frame­work build of Python, and alter­ing that instal­la­tion is, well, a bad idea. I don’t rec­om­mend it.

Now, some peo­ple may rec­om­mend you install mac­ports or fink: these are both “sorta” pack­age man­agers for OS/X, and while I do have mac­ports installed, I do not use it for python work. I pre­fer com­pi­la­tion and self man­age­ment, that and I’ve had issues with mac­ports in the past. So, go ahead and install it, but don’t use it for python work.

So, now you have xcode — fire up terminal.app, from now on, this is your best friend. When you fire it up, you’re in your /Users/username direc­tory — your home direc­tory. You want to look for one of the fol­low­ing files, .bashrc or .bash_profile. If the lat­ter doesn’t exist, do a “touch .bash_profile” — this will cre­ate an empty one for you, which you will need later on.

If you were to type “python” in right now, the default leop­ard install (2.5.1) would pop up. The site-packages direc­tory lives in /Library/Python/2.5/site-packages. If you were to start installing python mod­ules, that’s where they would go. But we’re not going to do that.

Head over to python.org — go to the down­load page and down­load the lat­est 2.6 release of python (2.6.1 right now). Unpack and install it — the installer will install this into Library/Frameworks/Python.framework/ — this is out­side of the default sys­tem install. It may install sym­bolic links to the bina­ries in /usr/local/bin, oth­er­wise scripts that come with installed pack­ages and the python binary itself go into /Library/Frameworks/Python.framework/Versions/2.6/bin.

The installer will also mod­ify your ~/.bash_profile we cre­ated to prepend this onto your PATH vari­able. If you view your ~/.bash_profile you should see a mod­i­fied ver­sion which adds the /usr/local/bin or the /Library/Frameworks/Python.framework/Versions/2.6/bin direc­tory to your path (it should be labeled with a comment).

Note, that if the installer doesn’t update your pro­file, sim­ple add this line:

export PATH=/Library/Frameworks/Python.framework/Versions/2.6/bin:/usr/local/bin:$PATH

I totally boned this ear­lier: Just to clar­ify, the down­loaded ver­sion of python installs sym­bolic links in /usr/local/bin which point to bina­ries in the /Library/Frameworks/Python.framework/Versions/2.6/bin — any other tools you install will place their bina­ries into that /Library/Frameworks/Python.framework/Versions/2.6/bin direc­tory as well (some might also sym­link into /usr/local/bin).

Do the fol­low­ing “. ~/.bash_profile” — this sources the pro­file and changes your envi­ron­ment. You only need to do this once for this win­dow, any time you open a new ter­mi­nal win­dow, this is done for you.

Now you have the lat­est and great­est python 2.6 installed. You still have the sys­tem install in the default loca­tion, and you can swap between either one by using an explicit path, for exam­ple “/usr/bin/python” loads the sys­tem version.

IDLE is installed into the /Applications/Python… direc­tory, if you need it.

So you have a new shiny install, and you’re ready to get started…

No!

If you started down­load­ing libraries and stuff to this new install you’d be taint­ing an oth­er­wise pris­tine instal­la­tion of python. No, you wouldn’t want to do that, would you?

Rather than taint it, we’re going to install a few depen­den­cies you’ll need an a handy tool called vir­tualenv. Trust me, you’ll thank me.

Most of the known python world uses easy_install (with setup­tools) to install pack­ages from the web. I pre­fer pip. To be effec­tive in the world, you’re going to want to install both, and only fall back to easy_install if pip fails you.

So, down­load this python script — save it to a tem­po­rary direc­tory, your down­loads folder, it doesn’t mat­ter. This is ez_setup.py, and will boot­strap setup­tools and easy_install for you — just run:

sudo python ez_setup.py

Once that’s com­plete, head over to pypi and down­load the pip tar­ball. Unpack it and exe­cute “sudo python setup.py install”.

Next up, well — let’s cheat — in ter­mi­nal, type:

sudo pip install virtualenv

This installs easy_setup and pip and vir­tualenv into the 2.6.1 install we installed pre­vi­ously. The bina­ries are installed to /Library/Frameworks/Python.framework/Versions/2.6/bin. Your egre­gious mod­i­fi­ca­tion of this pris­tine install is almost complete.

Next install virtualenvwrapper:

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sudo pip install virtualenvwrapper

The envi­ron­ment file is installed to /Library/Frameworks/Python.framework/Versions/2.6/bin/virtualenvwrapper_bashrc

Now edit your ~/.bash_profile and add two lines at the bottom:

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export WORKON_HOME=$HOME/virtualenvs
source /Library/Frameworks/Python.framework/Versions/2.6/bin/virtualenvwrapper_bashrc

Save it and then run “. ~/.bash_profile” — this will add the vir­tualenv com­mands to your envi­ron­ment. Hooray! This also sets the default direc­tory that they’re stored in to “~/virtualenvs”. Much vic­tory to be had. You should run “mkdir ~/virtualenvs” at this point.

So, we have the basics. Now, you’re going to want to make your default vir­tualenv, in ter­mi­nal type:

mkvirtualenv default

This will cre­ate a ~/virtualenvs/default vir­tual envi­ron­ment where you can poke around and begin to install juicy things into. Note your prompt changes to reflect the envi­ron­ment loaded. I have my .bash_profile set to load the default ver­sion when­ever I fire up terminal.app, for example:

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export WORKON_HOME=$HOME/virtualenvs
source $HOME/env_ext/virtualenvwrapper_bashrc
workon default

You can point editors/etc to point at this envi­ron­ment as well, bina­ries, libraries/etc are loaded into ~/virtualenvs/default/bin and ~/virtualenvs/default/lib for example.

You can install all sorts of good­ies, for exam­ple, if I wanted to cre­ate a pygame envi­ron­ment, I would do this:

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mkvirtualenv pygame
cd ~/virtualenvs/pygame
easy_install pygame

And then at any time, I could swap over to the pygame one with the “workon” com­mand pro­vided by vir­tualenv wrapper.

You can also cre­ate a vir­tual env pointed at the old sys­tem instal­la­tion — some­thing like this should do the trick:

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cd ~/virtualenvs
virtualenv -p /usr/bin/python python2.5.1

And then “workon python2.5.1″ will load the vir­tualenv point­ing at that inter­preter. Viola! You’ve man­aged to not taint the built in ver­sion, add a more recent ver­sion (mod­i­fy­ing it only a lit­tle) and add the abil­ity to rapidly swap envi­ron­ments. Hooray!

Astute read­ers might point out that adding the “to the side” install of python would remove access to the pyobjc bridge that ships with the built in ver­sion, you can pip/easy_install the objc libraries now: check out pypi. Also, adding the 2.5.1 vir­tualenv means you can hack on the shipped ver­sion of pyobjc as well.

I’d rec­om­mend ready the docs for vir­tualenv, vir­tualenv wrap­per, pip and easy_install so you under­stand how things actu­ally work, I’ve only cov­ered the basics here.

The down­loaded ver­sion of python doesn’t taint your sys­tem, it installs cleanly to the side of the built in ver­sion of python, any­thing past that point is shell hackery.

Side note
If you want a quick and dirty way of installing a more fea­ture rich ver­sion of read­line, you can also just run:

pip install readline

I’d also like to finally point out that this makes my life (I’m is run­ning the default + lat­est shipped 2.6 + lat­est shipped 3.0 + 2 ver­sions for python svn) life much eas­ier to deal with.

See also this write up by Kumar McMillan

In a com­plete tan­gent from my numer­ous other projects, I’ve had a few peo­ple ask me recently about python on the mac, how to get started/etc. I’m going to solely...