TweetFollow Us on Twitter

Mac in the Shell-Python on the Mac: PyObjC

Volume Number: 25
Issue Number: 06
Column Tag: Mac in the Shell

Mac in the Shell-Python on the Mac: PyObjC

Writing native Cocoa apps using Python

by Edward Marczak

Introduction

Over the last few months, we've been covering the basics of Python. Aside from a few OS X-specific issues raised in the first article (how to get the built-in docs working, etc.), you could really take the lessons learned anywhere - Linux, Windows, or any platform where you find a Python runtime. We needed those basics - and we have more to cover, certainly. However, this is MacTech. There's plenty that one can do with some very basic Python and Python/Objective-C bridge, letting you tap into Cocoa. Cocoa? Isn't that reserved for Obj-C developers? Nope. While MacTech has covered this concept before (Scott Corely, "Python Cocoa: Delicious," February 2009), I'd like to put together the lessons learned in this column along with a more utilitarian approach.

Read The Fine Manual

Anytime we're working with Cocoa and the technologies in OS X, we'll probably be pouring through the developer references at http://developer.apple.com. You'll need an ADC account to do so. Even the free variety will do, so, go sign up now if you haven't already!

Once you're logged into the Developer Connection, head to the developer docs at http://developer.apple.com/documentation/. More often than not, you'll search on the topic you're after. Sometimes, you find good documentation spread out over several categories. Today, we'll be looking at getting information out of Address Book. True to form, the docs are somewhat spread out. I'll make reference to each as I use it. In short, for now, just search on "address book".

Translating Obj-C

First, why would we want to do this? There are certainly cases when developing for OS X where straight Obj-C is the right choice. However, I'm taking this from a System Administrator's point of view. Often, a System Administrator is already writing basic scripts in bash. I love bash, but there's only so far that it'll get you without becoming painful. If you're writing a script in bash and it passes the 4 functions milestone, it may be time to consider a language more suited to your task. For example, bash isn't really great with databases.

Sure, you can use the mysql binary, pipe the output to awk, and manipulate results from there. But is that the best use of your time and talent? Ever deal with arrays in bash? Pain. While I may recommend Python or Ruby as a step up in general, these languages are made even more special under OS X thanks to Apple's inclusion of an Obj-C bridge. BridgeSupport opens up OS X's native APIs to Python, Ruby and JavaScript. This is available and standard on every Mac running 10.5 or higher. (10.4 support is available, but you'll need to install it yourself, which is outside the scope of this article). BridgeSupport deals with all of the behind-the-scenes work of converting between Python and the native frameworks. The first challenge to this technique is interpreting the documentation. We're going to code all of this in Python, and the docs are directed at people writing in C and Objective-C. Anyone remember having to translate Mac Toolbox API calls from Pascal to C? I digress...

Now that we've covered Python classes, you know about sending a message to an object using dot notation. In last month's column, the BankClass example class contained deposit and withdraw methods. A new class could be created and a method called in the following manner:

acct = Account('Joan', 'Smith')    # Create new account
acct1.Deposit(50)       # Note use of class method here

However, if we got this information from Apple's developer documentation, you'd see something like this:

[acct1 Deposit:50]

This was covered in depth in the "Python Cocoa: Delicious" article referenced earlier, but I'll cover the basic rules here.

As you can see, Obj-C uses square brackets to send messages to objects. The easiest call to translate is a simple message with no parameters. This:

[object message];

in Python becomes:

object.message()

When a method takes parameters, Obj-C places them in-line:

[object message:40 key:50];

Python keeps its usual format here, separating the method name and parameters. Each message and parameter gains a trailing underscore character:

object.message_key_(40,50)

Essentially, each colon is replaced by an underscore - even if there's only one parameter. For example:

object.message_(40)

To instantiate an objective-c class in the first place is fairly straightforward.

object = NSObject.alloc().init()

Let's see all of this in action.

Reading the Address Book

The beauty of using a language like Python is that you can author in any editor you like, save and run. This skips the compile/link phase so familiar to Obj-C developers. So, pull up your favorite editor-remember, too, that most editors will be able to recognize Python code and syntax color, indent properly and so on, for you-and let's go.

Contained in /System/Library/Frameworks/Python.frame-work/ are the modules that Python uses for BridgeSupport. These can simply be imported into Python. First thing is first, our magic shebang line:

#!/usr/bin/env python

(Remember, if you have multiple versions of python on your system for some reason, under 10.5, the built-in BridgeSupport only works with Python 2.5. If you need you need to explicitly call that version, then do so). From here, we'll import the AddressBook framework:

from AddressBook import *

It's rare that I like or use the 'from blah import *' style, but there are times when it makes perfect sense. This, I feel, is one of them. We talked extensively about imports and namespaces in previous articles.

Let's create a new instance of an address book object:

aBook = ABAddressBook.sharedAddressBook()

Painless, right? This returns the address book for the logged-in user. Keeping this simple, let's grab the 'me' card for the logged in user and print it out:

myRecord = aBook.me()
print myRecord

That's it! In 3 lines of code, we get a good amount of information. Here's the output:

ABPerson (0x1ab0a40) {
   ABPersonFlags  : 0
   ABRelatedNames : {
      *  child  Edward R Marczak
}
   Address       : {
      *  work  {
    City = Anytown;
    Country = USA;
    CountryCode = us;
    State = AA;
    Street = "555 Any Street";
    ZIP = 11111;
}
}
   AIMInstant     : {
      *  home  myaim
}
   Creation       : 2005-10-28 09:45:40 -0400
   Email          : {
      *  work  marczak@radiotope.com
}
   First          : Edward
   JobTitle       : Owner
   Last           : Marczak
   Middle         : R
   Modification   : 2009-01-14 11:11:25 -0500
   Organization   : Radiotope
   Phone          : {
      *  mobile  555-555-5185
        home    555 555-5370
        main    555-555-5489
}
   Title          : Mr.
   Unique ID      : B3AD0F6B-4AB8-4E84-82C4-BF1EB7475659:ABPerson
}

Each of the properties in the record can be accessed and iterated over individually. Each property has a unique name used for this purpose. An illuminating method of discovering this, besides the Apple documentation is to use the dir() function that we've seen previously. Save your work and open a new document that contains this simple code:

#!/usr/bin/env python
import AddressBook
x = dir(AddressBook)
for i in x:
  print i

When you run it, you'll get an absolute ton of output, so pipe it through less or use a GUI editor that can run the code in its own window. It'll look like this:

ABACE
ABACL
ABAccessibilityMockUIElement
ABAddPropertiesAndTypes
ABAddRecord
ABAddToGroupCommand
ABAddressAttributedString
ABAddressBook
...
kABAIMHomeLabel
kABAIMInstantProperty
kABAIMWorkLabel
kABAddressCityKey
kABAddressCountryCodeKey
kABAddressCountryKey
kABAddressHomeLabel
kABAddressProperty
kABAddressStateKey
...
kCFXMLTreeErrorLocation
kCFXMLTreeErrorStatusCode
kEventABPeoplePickerDisplayedPropertyChanged
kEventABPeoplePickerGroupDoubleClicked
kEventABPeoplePickerGroupSelectionChanged
kEventABPeoplePickerNameDoubleClicked
kEventABPeoplePickerNameSelectionChanged
kEventABPeoplePickerValueSelectionChanged
kEventClassABPeoplePicker
kEventParamABPickerRef
objc
protocols
super

This lists every function and constant definition in the framework. In this case, we're interested in the block where each constant has the 'kAB' prefix. Each of these properties represents a potential field in the address book record - not all must be present. So, how can we tell which fields are present in a given record? We can ask. Back to our original code!

Here's a complete Python solution to dumping the current user's Address Book, I'll explain the parts not yet covered after this code listing.

Listing 1: dumpAB.py

#!/usr/bin/env python
from AddressBook import *
aBook = ABAddressBook.sharedAddressBook()
for person in aBook.people():
  properties = person.allProperties()
  for prop in properties:
    if prop == "com.apple.ABPersonMeProperty":
      continue
    elif prop == "com.apple.ABImageData":
      continue
    print prop, ":", person.valueForProperty_(prop)
  print '-'*60
  print

The people() method returns an array (an NSArray, specifically-the Obj-C Bridge deals with converting between the Obj-C types and Python types). We've previously covered Python for loops, and this one is no different. This loop iterates over each entry returned by the people() method, assigning it to person in each iteration.

With each person, we use the allProperties() method to determine the properties contained in that record. Then, we use another for loop to print only those properties. Note the if statement in this block: there are two properties present in each record that we're really not going to do anything with. Using a continue statement lets us restart the loop at the top.

Now, this isn't going to win any coding competitions, but look at how simple it is. No compiler or special IDE was needed to generate or run any of this.

What Happened? (Maybe)

Some of you may have seen an error pop up while running this program. Something about a "UnicodeDecodeError". What happened? This, partially, is the old-school Unix ASCII-ness colliding with modern sensibilities. You'll only see this error if one of your address book entries has Unicode characters in it (accent marks, Asian/Hebrew/Russian character sets and so on). Well, OS X is built to deal with this. Now, this depends on the environment in which you ran this. Terminal.app should actually have no problem as it's Unicode compliant. Surprisingly, some GUI text editors still don't handle Unicode properly, or, just need a little help. One thing you can do is give the interpreter a little hint: immediately following the magic shebang line (#!/usr/bin/env python), include the following:

# encoding: utf-8

This explicitly sets the encoding of the document. Additionally, Python itself has built-in support for Unicode strings. When printing a string, prefix it with 'u' to specify Unicode output. Like this:

print u'This is a Unicode string'

If you're printing a variable, it's similarly easy:

print u'%s' % (variable)

This is just one of those things that OS X users expect, and script authors need to bear in mind. Kind of like spaces in filenames...

Conclusion

There are actually a few more things we can cover about the Obj-C Bridge and its use in Python. However, we accomplished our goal for this month, and I hope you can see how easy some of these basic tasks are. You'll find that there are often several ways of approaching the code when using BridgeSupport. The methods used in this article are the most appropriate for the task at hand. See the References section below for the specific AddressBook documentation that I used to determine the bulk of this.

If we were more ambitious here, we could certainly do more with the data returned. Like write it out as a CSV file. AddressBook also supports group information, which I actually use fairy often, but that's a topic for next month.

Media of the month: I know, I usually suggest a good book, movie or music CD here, but this month is a little different. This month's suggestion is the outdoors - don't forget about it! Seriously, I'm not really a 'sun person,' but it is nice to take a walk with no laptop/phone/electronic device. Take a bike ride. Have a picnic. Take a (real) hike. Experience it. Just don't forget that there's a world outside of the LCD that we often sit a foot or two away from.

Hopefully, you're reading this at Apple's (sold out, again!) WWDC. Most of us from MacTech are here too (and you may have received this issue while on line for the Keynote - welcome!). Ping us, stop us in the halls - just say hello! See you next month.

References

"Address Book Programming Guide for Mac OS X," http://developer.apple.com/documentation/userexperience/Conceptual/AddressBook/AddressBook.pdf

"ABAddressBook Class Objective-C Reference," hhttp://developer.apple.com/documentation/UserExperience/Reference/AddressBook/Classes/ABAddressBook_Class/ABAddressBook_Class.pdf

"ABPerson C Reference," http://developer.apple.com/documentation/UserExperience/Reference/AddressBook/C/ABPersonRef/ABPersonRef.pdf


Ed Marczak is the Executive Editor for MacTech Magazine, and has been lucky enough to have ridden the computing and technology wave from early on. From teletype computing to MVS to Netware to modern OS X, his interest was piqued. He has also been fortunate enough to come into contact with some of the best minds in the business. Ed spends his non-compute time with his wife and two daughters.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

How to get started with Prisma
If there's one thing people like to do more than taking pictures with their smartphones, it's tinkering with those photos in some way. Numerous apps have sprung up over the last several years that allow you to use filters and special effects to... | Read more »
6 Pokemon GO updates you can expect, acc...
Pokemon GO had a scheduled appearance at this year's San Diego Comic-Con for a while, but it was only relatively close to the show that it was upgraded to a spot in Hall H. That's the biggest venue at SDCC, one usually reserved for the largest... | Read more »
How to evolve Eevee in Pokemon GO
By now, almost everyone should be hip to how to evolve Pokemon in Pokemon GO (and if not, there's a guide for that). Just gather enough candy of the appropriate type, feed them all to the Pokemon, and evolution happens. It's a miracle that would... | Read more »
CSR Racing 2: Guide to all game modes
It might not seem like there are all that many ways to go fast in a straight line, but CSR Racing 2 begs to differ. [Read more] | Read more »
Bulb Boy (Games)
Bulb Boy 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Multi-award winning 2D point & click horror adventure about a boy with a glowing head. | Read more »
5 top free emoji keyboard apps
If we're not at peak emoji yet as a society, it feels like we definitely should be. The emoji concept has gone far beyond what anyone in Japan could have envisioned when the people there unleashed it on an unsuspecting world, but the West has... | Read more »
How to unlock more characters in Disney...
One of the big charms of Disney Emoji Blitz is seeing a wide variety of beloved Disney and Pixar characters transformed into smiling emojis. Even someone like the sneaky Randall from Monsters Inc., who probably never cracked a smile on film, is... | Read more »
Cubway (Games)
Cubway 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Cubway is a journey with an abstract story of lifecycle of rebirth, called Samsara. Guide the cube through the long way full of dangers... | Read more »
Colorcube (Games)
Colorcube 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Turn pieces and blend colours in this minimal yet visually stunning puzzler.Over 200 handcrafted and challenging levels. Features... | Read more »
Doodle God Griddlers (Games)
Doodle God Griddlers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

13-inch 1.6GHz/128GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/128GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $799.99 $200 off MSRP Their price is the... Read more
13-inch 1.6GHz/256GB MacBook Air on sale for...
Amazon has the 13″ 1.6GHz/256GB MacBook Air on sale for $200 off MSRP for a limited time. Shipping is free: - 13″ 1.6GHz/256GB MacBook Air (sku MMGG2LL/A): $999.99 $200 off MSRP Their price is the... Read more
Free iOS Business App notably* Helps Service...
PayStudio Inc. has introduced their new business app notably* 1.0, developed for iPhone and iPod touch. notably* was specifically developed to help service and trade professionals go digital and... Read more
27-inch iMacs on sale for $200 off MSRP
Amazon has 27″ iMacs on sale for $200 off MSRP including free shipping: - 27″ 3.3GHz iMac 5K: $2099 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $1799.99 $200 off MSRP - 27″ 3.2GHz/1TB HD iMac 5K... Read more
Mac Pros on sale for $200 off MSRP
B&H Photo has Mac Pros on sale for $200 off MSRP. Shipping is free, and B&H charges sales tax in NY only: - 3.7GHz 4-core Mac Pro: $2799, $200 off MSRP - 3.5GHz 6-core Mac Pro: $3799, $200... Read more
Save up to $600 with Apple refurbished Mac Pr...
Apple has Certified Refurbished Mac Pros available for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The following... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 3.1GHz iMac 4K: $1379 $120 off MSRP - 21″ 2.8GHz iMac: $1199.99 $100 off MSRP - 21″ 1... Read more
Charitybuzz Set to Auction Unique Apple-1 Com...
Offering an opportunity to own the computer that sparked a revolution, on Monday, July 25, leading online charity auction platform Charitybuzz will auction what is claimed to be the world’s most... Read more

Jobs Board

*Apple* Retail - Multiple Positions, Willow...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Evangelist - JAMF Software (United S...
The Apple Evangelist is responsible for building and cultivating strategic relationships with Apple 's small and mid-market business development field teams. This Read more
*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Professional Learning Specialist - A...
Job Summary The Apple Professional Learning Specialist is a full-time position for one year with Apple in the Phoenix, AZ area. This position requires a high Read more
*Apple* Picker - Apple Hill Orchard (United...
Apple Hill Orchard, Co. Rte. 21,Whitehall, NY 9/7/16-10/228/16. Pick fresh market or processing apples Productivity of 60 boxes and 80 boxes processing fruit per Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.