Looking at this error, are you using the xdot library by any chance?
I had to port this to Python3 and GTK3 a year or two ago for our application. I looked it up and this is the line in my xdot port with a special GTK3 comment that I had to change the type.
__gsignals__ = {
'clicked' : (GObject.SIGNAL_RUN_LAST, None, (str, object))
}