Python and C interaction - callback function

Question

I'm trying to make a key logger for Mac OS for one of my research projects. I have a C code which will grab keystroke and write them to a text file. (The following code I have taken out some not important stuff)

What I need to do now is just like PyHook, instead of write the data to a text file, to pass a Python callback function to the C code and make it passes back the key input to Python, so I can do necessary analysis with Python.

I have look for how to do it, but honestly I have no idea how to approach this, as I am not used to C programming or Python extensions. Any help would be greatly appreciated.

#include <Carbon/Carbon.h>
#include <ApplicationServices/ApplicationServices.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/time.h>

#define NUM_RECORDING_EVENT_TYPES 5
#define RECORD 0
#define MOUSEACTION 0
#define KEYSTROKE 1
// maximum expected line length, for fgets
#define LINE_LENGTH 80
#define kShowMouse TRUE

OSStatus RUIRecordingEventOccurred(EventHandlerCallRef nextHandler, EventRef theEvent, void *userData);

void prepareToRecord(); // install the event handler, wait for record signal

// note that keyboard character codes are found in Figure C2 of the document
// Inside Macintosh: Text available from http://developer.apple.com
char * keyStringForKeyCode(int keyCode); // get the representation of the Mac keycode

// Global Variables
int dieNow = 0;    // should the program terminate
int ifexit = 0;       // Exit state 
char *filename = NULL;  // Log file name
FILE *fd = NULL;   // Log file descriptor

int typecount = 0;          // count keystroke to periodically save to a txt file

struct timeval thetime;  // for gettimeofday
long currenttime;   // the current time in milliseconds

int main()
{
    filename = "test.txt";
    fd = fopen(filename, "a");

    // Get RUI ready to record or play, based off of mode
    prepareToRecord();

 return EXIT_SUCCESS;
}

// event handler for RUI recorder
OSStatus RUIRecordingEventOccurred(EventHandlerCallRef nextHandler, EventRef theEvent, void *userData)
{
 // Determine class and kind of event
    int eventClass = GetEventClass(theEvent);
    int eventKind = GetEventKind(theEvent);

    /* Handle Keyboard Events */
    if((eventClass == kEventClassKeyboard) && (eventKind == kEventRawKeyDown)) /* key release implied */ {
        int keyCode, modifiers;  // what did the user press? any modifier keys down?

  // gather keystroke information
        GetEventParameter(theEvent, kEventParamKeyCode, typeInteger, NULL, sizeof(keyCode), NULL, &keyCode);
        GetEventParameter(theEvent, kEventParamKeyModifiers, typeInteger, NULL, sizeof(modifiers), NULL, &modifiers);

        // What time is it?
        gettimeofday(&thetime, NULL);
        currenttime =(((thetime.tv_sec*1000000) + (thetime.tv_usec)));

  fprintf(fd, "%s\n", keyStringForKeyCode(keyCode));

    } 

    return EXIT_SUCCESS;
}


void prepareToRecord()
{
 EventRecord event;  // holds an event for examination

    // Types of events to listen for
    EventTypeSpec eventTypes[NUM_RECORDING_EVENT_TYPES] = {{kEventClassKeyboard, kEventRawKeyDown}};

 // Install the event handler
    InstallEventHandler(GetEventMonitorTarget(), NewEventHandlerUPP(RUIRecordingEventOccurred), NUM_RECORDING_EVENT_TYPES, eventTypes, nil, nil);

    // event loop - get events until die command
 do {
        WaitNextEvent((everyEvent),&event,GetCaretTime(),nil);
 } while (dieNow == 0);
}


char * keyStringForKeyCode(int keyCode)
{
 // return key char
 switch (keyCode) {
  case 0: return("a");
 default: return("Empty"); // Unknown key, Return "Empty"
 }
}

Answer 1

It's easy - Just Follow the instructions - Calling Python Functions from C (Update March 2022: for Python3, see the corresponding chapter in Extending and Embedding the Python Interpreter).

Alternatively if you are trying to call C/C++ functions from Python you can use SWIG or one of Python's module CTypes