In Pyside, why does emiting an integer > 0x7FFFFFFF result in "OverflowError" after the signal is processed?
pyside, python, qt, signals
Solution
I'm mostly a PyQt user, but I believe the behavior is similar. `int` in signal definition is mapped to 4-byte integer (as Qt understands an `int`).
One possible solution is to force the signal to emit a Python object. This works:
class Communicate(QObject):
speak = Signal(object)
But be aware that, if you connect this signal to a slot that expects a Qt's version of `int` (for example `QtGui.QSpinBox.setMaximum`) you'll see the same behavior. Other than that, using this signal purely on the Python side should be fine.
Problem
I'm attempting to use signals/slots with large integers ranging from 0 - 2^32-1. I've discovered something a little weird -- once I emit > 7FFFFFFF boundary, I get OverflowError exceptions thrown after the slot is run. I might expect this kind of overflow if I or QT were explicitly using a signed 32 bit integer in another language like C or C++--as we all know 0x80000000 wraps back to -2^31 in 2s complement notation. In python though, its just 2^32 without wrapping. My assumption when writing the code though was that this is python and that the built-in int can grow very large (maybe arbitrarilly so?) and that I don't explicitly need to define something as 32 or 64 bit or signed/unsigned. It would all just work. The code below demonstrates what I'm seeing (Python 2.7.2 (64 bit), Pyside 1.1.0, Windows 7) ``` from PySide.QtCore import * @Slot(int) def say(i): print "Say %i" % i class Communicate(QObject): speak = Signal(int) someone = Communicate() someone.speak.connect(say) someone.speak.emit(0x7FFFFFFF) #works fine someone.speak.emit(0x80000000) #OverflowError after slot "say" runs say(0x80000000) #works fine ``` The exact output is: ``` Say 2147483647 Say -2147483648 OverflowError Say 2147483648 ``` - Why does Qt seem to treat the signals/slots of type integer as if its dealing with signed 32 bit integers and not python built-in ints? - If this is a restriction of Qt, what can I do to mark the int as unsigned or make sure QT can deal with integers > 0x7FFFFFFF?