Is there a way to dynamically call an Objective C function from Python?
For example, On the mac I would like to call this Objective C function
[NSSpeechSynthesizer availableVoices]
without having to precompile any special Python wrapper module.
We can call a C function from Python program using the ctypes module.
PyObjC is a bridge between Python and Objective-C. It allows full featured Cocoa applications to be written in pure Python. It is also easy to use other frameworks containing Objective-C class libraries from Python and to mix in Objective-C, C and C++ source.
cdll loads libraries which export functions using the standard cdecl calling convention, while windll libraries call functions using the stdcall calling convention. oledll also uses the stdcall calling convention, and assumes the functions return a Windows HRESULT error code.
You really can't use C in Objective-C, since Objective-C is C. The term is usually applied when you write code that uses C structures and calls C functions directly, instead of using Objective-C objects and messages.
As others have mentioned, PyObjC is the way to go. But, for completeness' sake, here's how you can do it with ctypes, in case you need it to work on versions of OS X prior to 10.5 that do not have PyObjC installed:
import ctypes
import ctypes.util
# Need to do this to load the NSSpeechSynthesizer class, which is in AppKit.framework
appkit = ctypes.cdll.LoadLibrary(ctypes.util.find_library('AppKit'))
objc = ctypes.cdll.LoadLibrary(ctypes.util.find_library('objc'))
objc.objc_getClass.restype = ctypes.c_void_p
objc.sel_registerName.restype = ctypes.c_void_p
objc.objc_msgSend.restype = ctypes.c_void_p
objc.objc_msgSend.argtypes = [ctypes.c_void_p, ctypes.c_void_p]
# Without this, it will still work, but it'll leak memory
NSAutoreleasePool = objc.objc_getClass('NSAutoreleasePool')
pool = objc.objc_msgSend(NSAutoreleasePool, objc.sel_registerName('alloc'))
pool = objc.objc_msgSend(pool, objc.sel_registerName('init'))
NSSpeechSynthesizer = objc.objc_getClass('NSSpeechSynthesizer')
availableVoices = objc.objc_msgSend(NSSpeechSynthesizer, objc.sel_registerName('availableVoices'))
count = objc.objc_msgSend(availableVoices, objc.sel_registerName('count'))
voiceNames = [
ctypes.string_at(
objc.objc_msgSend(
objc.objc_msgSend(availableVoices, objc.sel_registerName('objectAtIndex:'), i),
objc.sel_registerName('UTF8String')))
for i in range(count)]
print voiceNames
objc.objc_msgSend(pool, objc.sel_registerName('release'))
It ain't pretty, but it gets the job done. The final list of available names is stored in the voiceNames
variable above.
2012-4-28 Update: Fixed to work in 64-bit Python builds by making sure all parameters and return types are passed as pointers instead of 32-bit integers.
Since OS X 10.5, OS X has shipped with the PyObjC bridge, a Python-Objective-C bridge. It uses the BridgeSupport framework to map Objective-C frameworks to Python. Unlike, MacRuby, PyObjC is a classical bridge--there is a proxy object on the python side for each ObjC object and visa versa. The bridge is pretty seamless, however, and its possible to write entire apps in PyObjC (Xcode has some basic PyObjC support, and you can download the app and file templates for Xcode from the PyObjC SVN at the above link). Many folks use it for utilities or for app-scripting/plugins. Apple's developer site also has an introduction to developing Cocoa applications with Python via PyObjC which is slightly out of date, but may be a good overview for you.
In your case, the following code will call [NSSpeechSynthesizer availableVoices]
:
from AppKit import NSSpeechSynthesizer
NSSpeechSynthesizer.availableVoices()
which returns
(
"com.apple.speech.synthesis.voice.Agnes",
"com.apple.speech.synthesis.voice.Albert",
"com.apple.speech.synthesis.voice.Alex",
"com.apple.speech.synthesis.voice.BadNews",
"com.apple.speech.synthesis.voice.Bahh",
"com.apple.speech.synthesis.voice.Bells",
"com.apple.speech.synthesis.voice.Boing",
"com.apple.speech.synthesis.voice.Bruce",
"com.apple.speech.synthesis.voice.Bubbles",
"com.apple.speech.synthesis.voice.Cellos",
"com.apple.speech.synthesis.voice.Deranged",
"com.apple.speech.synthesis.voice.Fred",
"com.apple.speech.synthesis.voice.GoodNews",
"com.apple.speech.synthesis.voice.Hysterical",
"com.apple.speech.synthesis.voice.Junior",
"com.apple.speech.synthesis.voice.Kathy",
"com.apple.speech.synthesis.voice.Organ",
"com.apple.speech.synthesis.voice.Princess",
"com.apple.speech.synthesis.voice.Ralph",
"com.apple.speech.synthesis.voice.Trinoids",
"com.apple.speech.synthesis.voice.Vicki",
"com.apple.speech.synthesis.voice.Victoria",
"com.apple.speech.synthesis.voice.Whisper",
"com.apple.speech.synthesis.voice.Zarvox"
)
(a bridged NSCFArray) on my SL machine.
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