Edge detection callback fails silently after upgrading RPi.GPIO to 0.7+

Direct Answer

RPi.GPIO 0.7+ does not require a different callback signature. The callable passed to GPIO.add_event_callback() must still accept exactly one positional argument—the GPIO channel number—just as it did in 0.6.x. There is no separate documented migration step for add_event_callback. The silent failure after upgrading is most often explained by two behavioral changes in 0.7+: edge events are dispatched from a background daemon thread, and detection timing can interact differently with mechanical switch bounce when bouncetime is omitted.

Confirmed Facts vs. Likely Explanation

Confirmed across versions: the callback contract is unchanged. A valid registration looks like this:

def button_callback(channel):
    print("Edge detected on GPIO", channel)

GPIO.add_event_detect(17, GPIO.FALLING,
                      callback=button_callback,
                      bouncetime=200)

Likely explanation (verify locally): if your callback is currently a lambda, a nested function, or a bound method, test it as a module-level function first. RPi.GPIO invokes the callable directly from its event thread, so scope should not matter in principle, but the 0.7+ threading refactor makes a module-level function the safest baseline to confirm. A second common cause is a missing bouncetime; without it, a mechanical button can generate multiple rapid edges that the detector may coalesce or drop, making the callback appear silent.

Steps to Restore Callbacks Without Downgrading

1. Define the callback at module level with the channel parameter.
2. Add bouncetime=200 (milliseconds) to add_event_detect to debounce the switch.
3. Keep the main thread alive with a sleep loop. The event dispatcher runs in a daemon thread, so if the main thread exits, the process ends immediately.
4. Confirm the edge polarity matches the hardware: with an internal pull-up, a button press to ground produces a GPIO.FALLING edge.

One Diagnostic That Changes the Recommendation

Is the callback currently defined as a lambda or inside another function? If yes, moving it to module level is the first change to test. If it is already module-level, the next step is to add bouncetime and verify that the main thread is not exiting before the edge occurs.