The most important usage of PyObjC is enabling programmers to create GUI applications using Cocoa libraries in pure Python.

Cocoa developers may also benefit, as tasks written in Python generally take fewer lines than the Objective-C equivalent.

PyObjC was rewritten in 2002. Notable additions include the ability to directly subclass Objective-C classes from Python and nearly complete support for the Foundation, App Kit and Address Book frameworks.

The syntax for these message expressions is inherited from Smalltalk, and appears as an object, called the receiver, placed to the left of the name of the message, or selector, and both are enclosed within a pair of square brackets (the square bracket syntax is not inherited from Smalltalk).

Intended to improve code readability, colons are placed within the selector such that when the required arguments are in place, the expression's intent is unambiguous: This is distinct from the syntax used in Python, and in many other languages, where an equivalent expression would read: Translating Objective-C selectors to Python method names is accomplished by replacing each colon with a single underscore and listing the arguments within a pair of parentheses at the end, as demonstrated above.