Pyobjus API tutorial

This part of documentation covers tutorials related to API of pyobjus

Using dylib_manager

You need to load code into pyobjus so it can actually find the appropriate class with the autoclass function.

Maybe you want to write some Objective C code, and you want to load it into pyobjus, or you want to use some exising .dylib or sommething similar.

These problems can be solved using the pyobjus dylib_manager. Currently it has a few functions, so let’s see what we can do with them.

make_dylib and load_dylib functions

For the first example, let’s say that we want to write our class in Objective C, and after that we want to load that class into pyobjus. Okay, let’s write a class:

#import <Foundation/Foundation.h>

@interface ObjcClass : NSObject {
- (void) printFromObjectiveC;

@implementation ObjcClass

- (void) printFromObjectiveC {
        printf("Hello from Objective C\n");


The next step is to make a .dylib for this class, and load that .dylib into pyobjus. Suppose that we have previously saved this code into an objc_lib.m file.

With pyobjus you can compile objc_lib.m into objc_lib.dylib in the following way:

make_dylib('objc_lib.m', frameworks=['Foundation'], options=['-current_version', '1.0'])

Here, we are asking pyobjus to link objc_lib.m with the Foundation framework, and that we want to set the -current_version option to 1.0. You can also specify others frameworks and options if you want by just adding these elements to array.

The previous command will create an objc_lib.dylib file in the same directory as the objc_lib.m file. If you want to save it to another directory or with a different name, you can call make_dylib in this way:

make_dylib('objc_lib.m', frameworks=['Foundation'], out='/path/to/dylib/dylib_name.dylib')

After you make a .dylib with make_dylib function, you can load the code from the .dylib into pyobjus on following way:


# or if you specified anothed loation and name for .dylib
# load_dylib('/path/to/dylib/dylib_name.dylib')

Great, we have created a .dylib, loaded it into pyobjus and can now use the ObjcClass from our objc_lib.m file:

ObjcClass = autoclass('ObjcClass')
o_instance = ObjcClass.alloc().init()

This will output with:

>>> Hello from Objective C

load_framework function

There often can be situations when you need to load classes into pyobjus which don’t belong to the Foundation framework. For example, say you want to load a class from the AppKit framework.

In these cases you can use the load_framework function of dylib_manager.

So let’s see one simple example of using this function:

from pyobjus.dylib_manager import load_framework, INCLUDE

You may wonder what INCLUDE is, and can we load all Frameworks in this way? So INCLUDE is an enum, which contains paths to various Frameworks. Currently, INCLUDE contains paths to the following frameworks:

Accelerate = '/System/Library/Frameworks/Accelerate.framework',
Accounts = '/System/Library/Frameworks/Accounts.framework',
AddressBook = '/System/Library/Frameworks/AddressBook.framework',
AGL = '/System/Library/Frameworks/AGL.framework',
AppKit = '/System/Library/Frameworks/AppKit.framework',
AppKitScripting = '/System/Library/Frameworks/AppKitScripting.framework',
AppleScriptKit = '/System/Library/Frameworks/AppleScriptKit.framework',
AppleScriptObjC = '/System/Library/Frameworks/AppleScriptObjC.framework',
AppleShareClientCore = '/System/Library/Frameworks/AppleShareClientCore.framework',
AppleTalk = '/System/Library/Frameworks/AppleTalk.framework',
ApplicationServices = '/System/Library/Frameworks/ApplicationServices.framework',
AudioToolbox = '/System/Library/Frameworks/AudioToolbox.framework',
AudioUnit = '/System/Library/Frameworks/AudioUnit.framework',
AudioVideoBridging = '/System/Library/Frameworks/AudioVideoBridging.framework',
Automator = '/System/Library/Frameworks/Automator.framework',
AVFoundation = '/System/Library/Frameworks/AVFoundation.framework',
CalendarStore = '/System/Library/Frameworks/CalendarStore.framework',
Carbon = '/System/Library/Frameworks/Carbon.framework',
CFNetwork = '/System/Library/Frameworks/CFNetwork.framework',
Cocoa = '/System/Library/Frameworks/Cocoa.framework',
Collaboration = '/System/Library/Frameworks/Collaboration.framework',
CoreAudio = '/System/Library/Frameworks/CoreAudio.framework',
CoreAudioKit = '/System/Library/Frameworks/CoreAudioKit.framework',
CoreData = '/System/Library/Frameworks/CoreData.framework',
CoreFoundation = '/System/Library/Frameworks/CoreFoundation.framework',
CoreGraphics = '/System/Library/Frameworks/CoreGraphics.framework',
CoreLocation = '/System/Library/Frameworks/CoreLocation.framework',
CoreMedia = '/System/Library/Frameworks/CoreMedia.framework',
CoreMediaIO = '/System/Library/Frameworks/CoreMediaIO.framework',
CoreMIDI = '/System/Library/Frameworks/CoreMIDI.framework',
CoreMIDIServer = '/System/Library/Frameworks/CoreMIDIServer.framework',
CoreServices = '/System/Library/Frameworks/CoreServices.framework',
CoreText = '/System/Library/Frameworks/CoreText.framework',
CoreVideo = '/System/Library/Frameworks/CoreVideo.framework',
CoreWiFi = '/System/Library/Frameworks/CoreWiFi.framework',
CoreWLAN = '/System/Library/Frameworks/CoreWLAN.framework',
DirectoryService = '/System/Library/Frameworks/DirectoryService.framework',
DiscRecording = '/System/Library/Frameworks/DiscRecording.framework',
DiscRecordingUI = '/System/Library/Frameworks/DiscRecordingUI.framework',
DiskArbitration = '/System/Library/Frameworks/DiskArbitration.framework',
DrawSprocket = '/System/Library/Frameworks/DrawSprocket.framework',
DVComponentGlue = '/System/Library/Frameworks/DVComponentGlue.framework',
DVDPlayback = '/System/Library/Frameworks/DVDPlayback.framework',
EventKit = '/System/Library/Frameworks/EventKit.framework',
ExceptionHandling = '/System/Library/Frameworks/ExceptionHandling.framework',
ForceFeedback = '/System/Library/Frameworks/ForceFeedback.framework',
Foundation = '/System/Library/Frameworks/Foundation.framework',
FWAUserLib = '/System/Library/Frameworks/FWAUserLib.framework',
GameKit = '/System/Library/Frameworks/GameKit.framework',
GLKit = '/System/Library/Frameworks/GLKit.framework',
GLUT = '/System/Library/Frameworks/GLUT.framework',
GSS = '/System/Library/Frameworks/GSS.framework',
ICADevices = '/System/Library/Frameworks/ICADevices.framework',
ImageCaptureCore = '/System/Library/Frameworks/ImageCaptureCore.framework',
ImageIO = '/System/Library/Frameworks/ImageIO.framework',
IMServicePlugIn = '/System/Library/Frameworks/IMServicePlugIn.framework',
InputMethodKit = '/System/Library/Frameworks/InputMethodKit.framework',
InstallerPlugins = '/System/Library/Frameworks/InstallerPlugins.framework',
InstantMessage = '/System/Library/Frameworks/InstantMessage.framework',
IOBluetooth = '/System/Library/Frameworks/IOBluetooth.framework',
IOBluetoothUI = '/System/Library/Frameworks/IOBluetoothUI.framework',
IOKit = '/System/Library/Frameworks/IOKit.framework',
IOSurface = '/System/Library/Frameworks/IOSurface.framework',
JavaFrameEmbedding = '/System/Library/Frameworks/JavaFrameEmbedding.framework',
JavaScriptCore = '/System/Library/Frameworks/JavaScriptCore.framework',
JavaVM = '/System/Library/Frameworks/JavaVM.framework',
Kerberos = '/System/Library/Frameworks/Kerberos.framework',
Kernel = '/System/Library/Frameworks/Kernel.framework',
LatentSemanticMapping = '/System/Library/Frameworks/LatentSemanticMapping.framework',
LDAP = '/System/Library/Frameworks/LDAP.framework',
MediaToolbox = '/System/Library/Frameworks/MediaToolbox.framework',
Message = '/System/Library/Frameworks/Message.framework',
NetFS = '/System/Library/Frameworks/NetFS.framework',
OpenAL = '/System/Library/Frameworks/OpenAL.framework',
OpenCL = '/System/Library/Frameworks/OpenCL.framework',
OpenDirectory = '/System/Library/Frameworks/OpenDirectory.framework',
OpenGL = '/System/Library/Frameworks/OpenGL.framework',
OSAKit = '/System/Library/Frameworks/OSAKit.framework',
PCSC = '/System/Library/Frameworks/PCSC.framework',
PreferencePanes = '/System/Library/Frameworks/PreferencePanes.framework',
PubSub = '/System/Library/Frameworks/PubSub.framework',
Python = '/System/Library/Frameworks/Python.framework',
QTKit = '/System/Library/Frameworks/QTKit.framework',
Quartz = '/System/Library/Frameworks/Quartz.framework',
QuartzCore = '/System/Library/Frameworks/QuartzCore.framework',
QuickLook = '/System/Library/Frameworks/QuickLook.framework',
QuickTime = '/System/Library/Frameworks/QuickTime.framework',
Ruby = '/System/Library/Frameworks/Ruby.framework',
RubyCocoa = '/System/Library/Frameworks/RubyCocoa.framework',
SceneKit = '/System/Library/Frameworks/SceneKit.framework',
ScreenSaver = '/System/Library/Frameworks/ScreenSaver.framework',
Scripting = '/System/Library/Frameworks/Scripting.framework',
ScriptingBridge = '/System/Library/Frameworks/ScriptingBridge.framework',
Security = '/System/Library/Frameworks/Security.framework',
SecurityFoundation = '/System/Library/Frameworks/SecurityFoundation.framework',
SecurityInterface = '/System/Library/Frameworks/SecurityInterface.framework',
ServerNotification = '/System/Library/Frameworks/ServerNotification.framework',
ServiceManagement = '/System/Library/Frameworks/ServiceManagement.framework',
Social = '/System/Library/Frameworks/Social.framework',
StoreKit = '/System/Library/Frameworks/StoreKit.framework',
SyncServices = '/System/Library/Frameworks/SyncServices.framework',
System = '/System/Library/Frameworks/System.framework',
SystemConfiguration = '/System/Library/Frameworks/SystemConfiguration.framework',
Tcl = '/System/Library/Frameworks/Tcl.framework',
Tk = '/System/Library/Frameworks/Tk.framework',
TWAIN = '/System/Library/Frameworks/TWAIN.framework',
vecLib = '/System/Library/Frameworks/vecLib.framework',
VideoDecodeAcceleration = '/System/Library/Frameworks/VideoDecodeAcceleration.framework',
VideoToolbox = '/System/Library/Frameworks/VideoToolbox.framework',
WebKit = '/System/Library/Frameworks/WebKit.framework',
XgridFoundation = '/System/Library/Frameworks/XgridFoundation.framework'

If the Framework path which you want to load isn’t present in the INCLUDE enum, you can specify it manually. Let’s say that the path to AppKit isn’t available via the INCLUDE enum. You could load the Framework in the following way:


Using struct types

Pyobjus currently support NSRange, NSPoint, NSSize and NSRect structures. They are defined via the ctypes.Structure type.

Consider the following. You have an Objective C class with the name ObjcClass and a useRange: method of that class which is defined in this way:

- (void) useRange:(NSRange)r {
    printf("location: %ld, length: %ld\n", r.location, r.length);

So, if you want to call this method from Python, you can do something like this:

from pyobjus.objc_py_types import NSRange
from pyobjus import autoclass

ObjcClass = autoclass('ObjcClass')
o_cls = ObjcClass.alloc().init()
range = NSRange(10, 20)

This will output:

>>> location: 10, length: 20

A simmilar situation occurs when returning and using Objective C structure types. Let’s say that our ObjcClass has another method with the name makeRange:

- (NSRange) makeRange {
    NSRange range;
    range.length = 123;
    range.location = 456;
    return range;

Using this method from Python is really simple. Let’s say that we have included it from the previous Python code example:

range = o_cls.makeRange()
print range.length
print range.location

And this will output:

>>> 123
>>> 456

As you can see, dealing with Objective C structs from pyobjus is simple.

Let’s see how to create a NSRect type:

point = NSPoint(30, 50)
size = NSSize(60, 70)
rect = NSRect(point, size)

Dealing with pointers

As you know, C has a very powerful feature with name pointers. Objective C is a superset of the C language, so Objective C also has this great feature.

But wait, we are using Python, so how we can deal with pointers from Python???

Passing pointers

Relax, pyobjus is doing that job for you. I think the best way to explain is to show some concrete examples of that. So, let’s expand our ObjcClass class with another method:

- (void) useRangePtr:(NSRange*)r_p {
    NSRange r = r_p[0];
    printf("location: %ld, length: %ld\n", r.location, r.length);

In previous examples you have seen how to create an NSRange from Python, and you have sent values of the NSRange type. But now we have a situation when the method accepts a pointer to that type.

With pyobjus, you can call a method in the following way:

range = NSRange(40, 80)

And this will output:

>>> location:40, length: 80

So what has happened here? We pass the argument in the same way as with the useRange: method.

Pyobjus knows if a method accepts pointers to a type, or accepts values of that type. If a method accepts a pointer to a type, pyobjus will make a pointer to that type, point it to your type and pass that pointer to the method for you. So with this, you don’t need to care whether argument types are pointers or values.

You can also return pointers to types from Objective C methods. Let’s add another method to ObjcClass:

- (NSRange*) makeRangePtr {
    NSRange *r_p = malloc(sizeof(NSRange));
    NSRange r;
    r.length = 123;
    r.location = 567;
    *r_p = r;
    return r_p;

As you can see, this method creates a NSRange pointer, assigns a value to it, and at the end, it returns a pointer to the user. From Python, you can consume this method in this way:

range_ptr = o_cls.makeRangePtr()
# let we see actual type of returned object
print range_ptr

This will output following:

>>> <pyobjus.ObjcReferenceToType object at 0x10f34bcb0>

So here we can see another type -> ObjcReferenceToType. When we have a method which returns a pointer to some type, pyobjus will wrap that pointer with an ObjcReferenceToType object. This object contains the actual address of the C pointer. We can now pass that type to a function which accepts pointers.


# note that range_ptr is of ObjcReferenceToType type

But you may now wonder how to dereference the pointer to get the actual value?

The answer using the dereference function.

Dereferencing pointers

To dereference a pointer we use the dereference function:

from pyobjus import dereference

If a function returns a pointer to some known type, in other words, the return type isn’t void*, you can use the dereference function in this way:

range_ptr = o_cls.makeRangePtr()
range = dereference(range_ptr)

Pyobjus will extract the return type from the method signature, and will thus know which type to convert the pointer value to. If it returns a void pointer, you will need to specify the type which you want pyobjus to convert the actual value to.

Consider adding this method:

- (void*) makeIntVoidPtr {
    int *a = malloc(sizeof(int));
    *a = 12345;
    return (void*)a;

Now we can retrieve the value and dereference it:

int_ptr = o_cls.makeIntVoidPtr()
int_val = dereference(int_ptr, of_type=ObjcInt)
print int_val

This will output with:

>>> 12345

Notice that you can specify the of_type optional argument even though the method returns a NSRange pointer. With this, you can be sure that pyobjus will convert the value to that type.

Here is the list of possible types:


Those already listed types are defined inside the pyobjus module, so you can import them in the following way:

from pyobjus import ObjcChar, ObjcInt # etc...

Inside the pyobjus.objc_py_types module we define the struct and union types. Here is a list of them:


You can import them with:

from pyobjus.objc_py_types import NSRange # etc...

Objective C <-> pyobjus literals

If you are familiar with Objective C literals, then you know that they are a great feature, because literals reduce the amount of code you write. You may wonder is there some equvivalent with pyobjus. The answer is YES.

The next example illustrates how to use pyobjus literals, and what their Objective C equivalents are:

from pyobjus import *

# The following examples demonstrate the pyobjus literals feature
# The first line denotes native objective c literals, and the second pyobjus literals

# NSNumber *theLetterZ = @'Z';          // equivalent to [NSNumber numberWithChar:'Z']

# NSNumber *fortyTwo = @42;             // equivalent to [NSNumber numberWithInt:42]

# NSNumber *fortyTwoUnsigned = @42U;    // equivalent to [NSNumber numberWithUnsignedInt:42U]

# NSNumber *fortyTwoLong = @42L;        // equivalent to [NSNumber numberWithLong:42L]

# NSNumber *fortyTwoLongLong = @42LL;   // equivalent to [NSNumber numberWithLongLong:42LL]

# NSNumber *piFloat = @3.141592654F;    // equivalent to [NSNumber numberWithFloat:3.141592654F]

# NSNumber *piDouble = @3.1415926535;   // equivalent to [NSNumber numberWithDouble:3.1415926535]

# NSNumber *yesNumber = @YES;           // equivalent to [NSNumber numberWithBool:YES]

# NSNumber *noNumber = @NO;             // equivalent to [NSNumber numberWithBool:NO]

# NSArray *array = @[ @"Hello", NSApp, [NSNumber numberWithInt:42] ];
objc_arr(objc_str('Hello'), objc_str('some str'), objc_i(42))

# NSDictionary *dictionary = @{
#    @"name" : NSUserName(),
#    @"date" : [NSDate date],
#    @"processInfo" : [NSProcessInfo processInfo]
# };
    'name': objc_str('User name'),
    'date': autoclass('NSDate').date(),
    'processInfo': autoclass('NSProcessInfo').processInfo()

# NSString *string = @"some string";
objc_str('some string')

We have tried to make the build names for these literals clear and intuitive. We start with the prefix objc_ followed by the letter/letters which denote the Objective C type. For example, i for int, f for float, arr for NSArray, dict for NSDictionary, etc...

Unknown types

Let’s say that we have defined the following structures in our ObjcClass.

Note that we haven’t specified a type name for the structs, so their types will be missing from any method signatures which use them:

typedef struct {
    float a;
    int b;
    NSRect rect;
} unknown_str_new;

typedef struct {
    int a;
    int b;
    NSRect rect;
    unknown_str_new u_str;
} unknown_str;

Let’s play. Suppose that we have defined the following Objective C methods:

- (unknown_str) makeUnknownStr {
    unknown_str str;
    str.a = 10;
    str.rect = NSMakeRect(20, 30, 40, 50);
    str.u_str.a = 2.0;
    str.u_str.b = 4;
    return str;

The purpose of this method is to create an unknown type struct and add some values to it’s members. If you look at the debug logs from pyobjus, you will notice that the method returns the following type:


From this we can see that method returns some type which contains two integers and two structs. One struct is a CGRect, and another is some unknown type which contains a float, an integer and a CGRect struct. So, if the user hasn’t defined this struct, pyobjus can generate the type for them. Let’s call this function:

ret_type = o_cls.makeUnknownStr()

But wait, how will pyobjus know about the field names in the struct, because from the method signature we see only types, not actual names? Well, pyobjus will generate some ‘random’ names in alphabetical order.

In our case, the first member will have the name ‘a’, the second the name ‘b’ and the third the name CGRect. CGRect is used because it can help the user as an indicator of actual type if it is missing. The last one is another unknown type, so pyobjus will generate the name ‘c’.

Notice that in the case of the CGRect, it will have origin and size members because it is already defined so we know about these. This is not true for the last member, and pyobjus will thus choose the next alphabetical name for this member.

Perhaps you are asking yourself how you would know what the actual generated name is? Pyobjus will help you with this. There is a getMembers function which returns the name and types of some of the fields in the struct:

print ret_type.getMembers()

Python will output:

>>> [('a', <class 'ctypes.c_int'>), ('b', <class 'ctypes.c_int'>), ('CGRect', <class 'pyobjus.objc_py_types.NSRect'>), ('c', <class 'pyobjus.objc_py_types.UnknownType'>)]

If you want to provide your field names, you can do it this way:

ret_type = o_cls.makeUnknownStr(members=['first', 'second', 'struct_field', 'tmp_field'])

And if we now run the getMembers command, it will return this:

[('first', <class 'ctypes.c_int'>), ('second', <class 'ctypes.c_int'>), ('struct_field', <class 'pyobjus.objc_py_types.NSRect'>), ('tmp_field', <class 'pyobjus.objc_py_types.UnknownType'>)]

If you don’t need types, only names, you can call method in following way:

print ret_type.getMembers(only_fields=True)

Python will output:

>>> ['a', 'b', 'CGRect', 'c']

Also, if you want to know only names, you can do that the following way:

print ret_type.getMembers(only_types=True)

Python will output:

>>> [<class 'ctypes.c_int'>, <class 'ctypes.c_int'>, <class 'pyobjus.objc_py_types.NSRect'>, <class 'pyobjus.objc_py_types.UnknownType'>]

If you want to use the returned type to pass it as an argument to some function, there might be some problems. Pyobjus uses ctypes structures, so we can get the actual pointer to the C structure from Python objects, but if we want to get the correct values of the passed arg, we need to cast the pointer to the appropriate type.

If the type is defined in pyobjus/objc_cy_types.pxi, pyobjus will convert it for us, but if it isn’t, we will need to convert it manually. For example, inside any Objective C methods where we are passing the struct value. Lets see an example of this:

- (void) useUnknownStr:(void*)str_vp {
    unknown_str *str_p = (unknown_str*)str_vp;
    unknown_str str = str_p[0];
    printf("%f\n", str.rect.origin.x);

And from Python:


And Python will output with:

>>> 20.00

Using class

As you know, class is a Python keyword, so that might be a problem.

Let’s say that we want to get the Class type for an NSString instance...

We can use following:

NSString = autoclass('NSString')
text = NSString.alloc().init()

This will return:

<pyobjus.ObjcClass object at 0x1057361b0>

So, now we can use the isKindOfClass: method:


This will output True. Let’s see another example:

NSArray = autoclass('NSArray')

And this will output False.

So, as you can see, if you want to use class with pyobjus, you will need to use the some_object.oclass() method.

Using @selector

There may be situations when you need to use @selector, which is an Objective C feature. With pyobjus you can also get the SEL type for a method. Let’s say that we want to get the SEL for the init method:

from pyobjus import selector

This will output:

<pyobjus.ObjcSelector object at 0x1057361c8>

So, instead of using @selector(init) with Objective C, you can use selector('init') with pyobjus and Python to get the SEL type for that method (in this case the ‘init’ method).

If you want get the SEL for initWithUTF8String: you can use:


Other cases are the same for all methods.

Using @protocol

Objective C protocols provide what other languages call interfaces. They specify a list of methods which should be implemented in order to support that protocol.

Protocols define the interface which is then usually implemented by a delegate. Pyobjus provides us with the protocol decorator to handle this, enabling us to use Python objects as delegates:


Pyobjus will firstly try to use runtime introspection to determine the protocol methods. If this fails, it will revert to the list of protocols contained in the pyobjus/ file in your pyobjus checkout folder. Of course, many libraries define their own protocols, so cannot be included by default. For a complete list of protocols available on you system, run the tools/ file and then rebuild pyobjus (as per the install).

So, how do we use this decorator? We add functions with names that correspond to the protocol method names, then decorate these functions with the required protocol:

def connection_didFailWithError_(self, connection, error):

Here, we specify that our object method connection_didFailWithError_ handles the connection:didFailWithError: delegation of the NSURLConnectionDelegate protocol. Pyobjus then redirects this Objective-C message to our method.

For a complete example, please see the examples/ file.

Using enum types

Pyobjus currently supports NSComparisonResult and NSStringEncoding enums. If you want to use any others, you need to expand pyobjus with additional types by adding then to the pyobjus/ file.

But, let’s first see how to use the supported enum types with pyobjus. Consider the following example:

from pyobjus import autoclass, objc_str
from pyobjus.objc_py_types import NSComparisonResult

def enum_example():
    text = objc_str('some text')
    text_to_compare = objc_str('some text')
    if text.compare_(text_to_compare) == NSComparisonResult.NSOrderedSame:
        print 'the same strings'

    text_to_compare = objc_str('text')
    if text.compare_(text_to_compare) == NSComparisonResult.NSOrderedAscending:
        print 'NSOrderedAscending strings'

if __name__ == '__main__':

You can see that we use the NSComparisonResult enum in the above example to compare two strings. The Enum is defined in this way:

NSComparisonResult = enum("NSComparisonResult", NSOrderedAscending=-1, NSOrderedSame=0, NSOrderedDescending=1)

The first argument of the enum function is the name of new enum type, and the rest of the arguments are the field declarations of that enum. As you can see it is pretty simple to declare enum’s with pyobjus, so you can add new enum types to pyobjus. Keep in mind you will bo re-compile pyobjus is order to see these changes in your Python environment.

Using vararg methods

Objective C supports vararg (Variable Arguments) methods, so it would be great if you could use vararg methods from pyobjus. Fortunately, you can.

Let’s we say that we want to use the arrayWithObjects: method, which is a varargs method:

from pyobjus import autoclass, objc_str

NSArray = autoclass('NSArray')
array = NSArray.arrayWithObjects_(objc_str('first string'), objc_str('second string'), None)

text = array.objectAtIndex_(1)
print text.UTF8String()

Note that the last argument of a varargs methods must be None.

Using C array

In this section we will explain how to use a C array from pyobjus.

Let’s say that we made a library CArrayTestlib.dylib which contains test functions for a C array. Let’s load it:

import ctypes
from pyobjus import autoclass, selector, dereference, CArray, CArrayCount
from pyobjus.dylib_manager import load_dylib

load_dylib('CArrayTestlib.dylib', usr_path=False)
CArrayTestlib = autoclass("CArrayTestlib")
_instance = CArrayTestlib.alloc()

Now we can call the setIntValues: method:

- (void) setIntValues:(int[10])val_arr
    NSLog(@"Setting int array values...");
    memcpy(self->values, val_arr, sizeof(int) * 10);
    NSLog(@"Values copied...");

in this way:

nums = [0, 2, 1, 5, 4, 3, 6, 7, 8, 9]
array = (ctypes.c_int * 10)(*nums)

We can also return array values from this function:

- (int*) getIntValues
    if (!self->values)
        NSLog(@"Values have not been set.");
        return NULL;
        return self->values;

and consume them this way:

returned_PyList = dereference(_instance.getIntValues(), of_type=CArray, return_count=10)
print returned_PyList

Note that here we passing a return_count optional argument, which holds the number of array items which are returned from the getIntValues method.

But what if we don’t know the array count? In that case we need to have some argument in which the method will put the array count value.

Consider following method:

- (int*) getIntValuesWithCount:(unsigned int*) n
    NSLog(@" ... ... [+] getIntValuesWithCount(n=%zd)", n);
    NSLog(@" ... ... [+] *n=%zd", *n);
    if (!self->values)
        NSLog(@"Values have not been set");
        return NULL;
        *n = 10;
        NSLog(@" ... ... [+] getIntValuesWithCount(n=%zd)", n);
        NSLog(@" ... ... [+] *n=%zd", *n);
        return self->values;

The first argument of this function will contain the array count when the return statement is reached. So let’s call it:

returned_PyList_withCount = dereference(_instance.getIntValuesWithCount_(CArrayCount), of_type=CArray)
print returned_PyList_withCount

Pyobjus will internally read from that argument and convert the returned C array into a python list.

If the method returns values/an array count over reference or you don’t provide CArrayCount in the right position in the method signature, you will get an IndexError: tuple index out of range or segmentation fault, so don’t forget to provide CArrayCount in the right position.

You may wonder, can you use multidimensional arrays from pyobjus? Yes, you can. Consider following method:

- (void) set2DIntValues: (int[10][10]) val_arr
    NSLog(@"Setting 2D int array values...");
    memcpy(self->int_2d_arr, val_arr, sizeof(int) * 10 * 10);
    NSLog(@"Values copied...");
- (int*) get2DIntValues
    if (!self->int_2d_arr)
        NSLog(@"Values have not been set for int 2d array.");
        return NULL;
        return (int*)self->int_2d_arr;

To call this method first we need to make a multidimensional array from python using nested lists:

twoD_array = [
    [1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
    [11, 12, 13, 14, 15, 16, 17, 18, 19, 20],
    [21, 22, 23, 24, 25, 26, 27, 28, 29, 30],
    [31, 32, 33, 34, 35, 36, 37, 38, 39, 40],
    [41, 42, 43, 44, 45, 46, 47, 48, 49, 50],
    [51, 52, 53, 54, 55, 56, 57, 58, 59, 60],
    [61, 62, 63, 64, 65, 66, 67, 68, 69, 70],
    [71, 72, 73, 74, 75, 76, 77, 78, 79, 80],
    [81, 82, 83, 84, 85, 86, 87, 88, 89, 90],
    [91, 92, 93, 94, 95, 96, 97, 98, 99, 100]

This represents an int[10][10] array, so let’s call the above method:

returned_2d_list = dereference(_instance.get2DIntValues(), of_type=CArray, partition=[10,10])
print returned_2d_list

Note the optional partition argument of the dereference function. This argument contains the format of the C array, in this case [10, 10].

You can find additional examples on this link.