Python for Bioinformatics: NSTask

Thursday, August 7, 2008

NSTask

My initial attempts to include a C program file in a Cocoa-Python XCode project haven't worked. However, I do have a working example of using NSTask to run a C program as a separate process. I don't know if there is any advantage to doing it the Cocoa way (as opposed to using subprocess.Popen). The code in the AppDelegate is:

class PyXAppDelegate(NSObject):
    def applicationDidFinishLaunching_(self, sender):
        NSLog("Application did finish launching.")
        
        argL = ['13', '47', '36']
        #p = NSHomeDirectory() + '/Desktop/example'
        p = NSBundle.mainBundle().pathForResource_ofType_('example', None)
        #print 'path', p
        
        t = NSTask.alloc().init()
        t.setLaunchPath_(p)
        t.setArguments_(argL)
        
        cent = NSNotificationCenter.defaultCenter()
        cent.addObserver_selector_name_object_(
            self, 
            "checkATaskStatus:",
            NSTaskDidTerminateNotification,
            None)
        
        t.launch()
    
    @objc.signature('v@:@')
    def checkATaskStatus_(self, notification):
        status = notification.object().terminationStatus()
        if status == 0:     print 'success'
        else:               print 'error'

The C file looks (amost) like this:

#include < stdio.h>
#include < stdlib.h>
#include < string.h>
#include < math.h>

int isPrime(int x) {
 int i;
 float limit = sqrt(x) + 1;
 for (i = 2; i < limit; i++) {
  if (!(x % i)) return 0;
 } 
 return 1;
}

int main(int argc, char *argv[])
{
    printf("number of args = %i \n", argc);
    printf ("path %s\n", argv[0]);
    int i;
    for (i = 1; i < argc; i++) {
        printf("arg #%i, ", i);
        int x = atoi(argv[i]);
        printf("x = %i, ", x);
        printf("isPrime = %i\n", isPrime(x));
    }
    return 0;
}

It's compiled in the usual way

tom-elliotts-mac-mini-2:~ telliott_admin$ gcc example.c -o example

and then can be placed in a convenient directory, or more flexibly, added to the project. Notable, pathForResource_ofType_ will take 'None' for the second argument.

This is what it prints to the Console:

2008-08-07 19:44:05.325 PyX[3207:10b] Application did finish launching.
number of args = 4 
path /Users/telliott_admin/Cocoa.PyObjC/PyX/build/Release/PyX.app/Contents/Resources/example
arg #1, x = 13, isPrime = 1
arg #2, x = 47, isPrime = 1
arg #3, x = 36, isPrime = 0
success