The example given in the pynput documentation is:

def darwin_intercept(event_type, event):
    import Quartz
    length, chars = Quartz.CGEventKeyboardGetUnicodeString(
        event, 100, None, None)
    if length > 0 and chars == 'x':
        # Suppress x
        return None
    else:
        return event

But how to suppress function keys, e.g., the control key (who doesn’t have an Unicode equivalent)?
I tried simply replacing chars == 'x' by virtualKey == 0x37, but got an error message…