New-style signal/slot ********************* The new-style signal/slot was introduced by Riverbank on its PyQt v4.5. The main goal of this new-style is to provide a more pythonic syntax to the Python programmers. PySide uses `PSEP100 `_ as its implementation guideline. Old way: SIGNAL() and SLOT() ---------------------------- Both QtCore.SIGNAL(...) and QtCore.SLOT(...) macros allow Python to interface with Qt mechanisms. This is the old way of using signals/slots. The example below uses the well known *clicked* signal from a *QPushButton*. The *connect* method has a non python-friendly syntax. It is necessary to inform the object, its signal (via macro) and a slot to be connected to. :: ... def someFunc(): print "someFunc has been called!" ... button = QtGui.QPushButton("Call someFunc") QtCore.QObject.connect(button, QtCore.SIGNAL('clicked()'), someFunc) ... Next section shows how everything has changed to become more pythonic. New way: Signal() and Slot() ---------------------------- The new-style uses a different syntax to create and to connect signals/slots. The previous example could be rewritten as: :: ... def someFunc(): print "someFunc has been called!" button = QtGui.QPushButton("Call someFunc") button.clicked.connect(someFunc) ... Using QtCore.Signal() --------------------- Signals can be defined using the *QtCore.Signal()* class. Python types and C types can be passed as parameters to it. If you need to overload it just pass the types as tuples or lists. Besides that it can receive also a named argument *name* that defines the signal name. If nothing is passed as *name* then the new signal will have the same name as the variable that it is being assigned to. The section `Putting everything together`_ has a collection of examples that shows a bunch of situation using the *Signal()* class. **Note**: Signals should be defined only inside classes inheriting from QObject. This way the signal information is added to the class QMetaObject structure. Using QtCore.Slot() ------------------- Slots are assigned and overloaded using the decorator *QtCore.Slot()*. Again, to define a signature just pass the types like the *QtCore.Signal()* class. Unlike the *Signal()* class, to overload a function you don't pass every variation as tuple or list. Instead of that you have to define a new decorator for every different signature. The examples section below will make it clearer. Another difference is about its keywords. *Slot()* accepts a *name* and a *result*. The *result* keyword defines the type that will be returned and can be a C or Python type. The *name* behaves the same way as in *Signal()*. If nothing is passed as *name* then the new slot will have the same name as the function that is being decorated. Putting everything together --------------------------- Nothing better than examples to show how to use the new-style. Here you can find some code covering a good range of cases, from basic connections to more complex situations. - **Hello World example**: the basic example, showing how to connect a signal to a slot without any parameters. :: import sys from PySide import QtCore, QtGui # define a function that will be used as a slot def sayHello(): print 'Hello world!' app = QtGui.QApplication(sys.argv) button = QtGui.QPushButton('Say hello!') # connect the clicked signal to the sayHello slot button.clicked.connect(sayHello) button.show() sys.exit(app.exec_()) - **Lets add some arguments**: this is a modified *Hello World* version. It adds some arguments to the slot and creates a new signal. :: import sys from PySide import QtCore # define a new slot that receives a string and has # 'saySomeWords' as its name @QtCore.Slot(str) def saySomeWords(words): print words class Communicate(QtCore.QObject): # create a new signal on the fly and name it 'speak' speak = QtCore.Signal(str) someone = Communicate() # connect signal and slot someone.speak.connect(saySomeWords) # emit 'speak' signal someone.speak.emit("Hello everybody!") - **Lets add some overloads**: a little more modification on the previous example now including overloads. :: import sys from PySide import QtCore # define a new slot that receives a C 'int' or a 'str' # and has 'saySomething' as its name @QtCore.Slot(int) @QtCore.Slot(str) def saySomething(stuff): print stuff class Communicate(QtCore.QObject): # create two new signals on the fly: one will handle # int type, the other will handle strings speakNumber = QtCore.Signal(int) speakWord = QtCore.Signal(str) someone = Communicate() # connect signal and slot properly someone.speakNumber.connect(saySomething) someone.speakWord.connect(saySomething) # emit each 'speak' signal someone.speakNumber.emit(10) someone.speakWord.emit("Hello everybody!") - **Lets complicate even more**: now with overloads and complicated connections and emissions. :: import sys from PySide import QtCore # define a new slot that receives an C 'int' or a 'str' # and has 'saySomething' as its name @QtCore.Slot(int) @QtCore.Slot(str) def saySomething(stuff): print stuff class Communicate(QtCore.QObject): # create two new signals on the fly: one will handle # int type, the other will handle strings speak = QtCore.Signal((int,), (str,)) someone = Communicate() # connect signal and slot. As 'int' is the default # we have to specify the str when connecting the # second signal someone.speak.connect(saySomething) someone.speak[str].connect(saySomething) # emit 'speak' signal with different arguments. # we have to specify the str as int is the default someone.speak.emit(10) someone.speak[str].emit("Hello everybody!") PyQt compatibility ------------------ PyQt uses a different naming convention to its new signal/slot functions. In order to convert any PyQt script that uses this new-style to run with PySide just use one the proposed modifications below: :: from PySide.QtCore import Signal as pyqtSignal from PySide.QtCore import Slot as pyqtSlot or :: QtCore.pyqtSignal = QtCore.Signal QtCore.pyqtSlot = QtCore.Slot This way any call to *pyqtSignal* or *pyqtSlot* will be translated to a *Signal* or *Slot* call.