Mockup of observer pattern in Python and C

observer.c

// Observer pattern in C

#include <stdio.h>

// To pass and store functions, we need to define a function pointer
typedef void (*Signal)();

// We can the use this Signal as type for the contents of the `subscribers` array.
// We also keep track of how many subscribers there are currently, so as to
// not overwrite previously added signals.
int current = 0;
Signal subscribers[10];  // Only 10 subscribers are allowed at a time

// Make sure there is enough room for another subscriber
// then append the passed signal to the list of subscribers.
void connect(Signal signal) {
    if(current <= 10) {
        ++current;
        subscribers[current] = signal;
    }
    else
        printf("Sorry, max number of subscribers reached");
}


// Test signals
void signalA(char *message) {
    printf("SIGNAL A: %s\n", message);
}


void signalB(char *message) {
    printf("SIGNAL B: %s\n", message);
}


void slot() {
    // Slot to trigger connected signals, passing `argument`
    for(int i = 0; i < sizeof(subscribers) / sizeof(Signal); ++i)     {
        Signal subscriber = subscribers[i];
        if(subscriber)
            subscriber("Hello");
    }
}


int main(int argc, char *argv[]) {
    connect(signalA);
    connect(signalB);
    slot();
    return(0);
    // outputs: "SIGNAL A: Hello\nSIGNAL B: Hello"
}

observer.py

"""Observer pattern in Python"""


# Global list of connected signals
subscribers = []


def connect(signal):
    """Helper function for global list of signals"""
    subscribers.append(signal)


def slot(argument):
    """Slot to trigger connected signals, passing `argument`"""
    for subscriber in subscribers:
        subscriber(argument)


# Test signals
def signal_a(message):
    print("SIGNAL A: %s" % message)


def signal_b(message):
    print("SIGNAL B: %s" % message)


if __name__ == '__main__':
    connect(signal_a)
    connect(signal_b)
    slot("Hello")
    # outputs: "SIGNAL A: Hello\nSIGNAL B: Hello"