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 http://pybojc.sourceforge.net.
The standard Python GUI toolkit is Tkinter, based on the cross-platform Tk toolkit (http://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 http://www.activestate.com; it can also be built from source.
wxPython is another popular cross-platform GUI toolkit that runs natively on Mac OS X. Packages and documentation are available from http://www.wxpython.org.
PyQt is another popular cross-platform GUI toolkit that runs natively on Mac OS X. More information can be found at http://www.riverbankcomputing.co.uk/pyqt/.
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