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building compiling and installing PySide
New-style signal/slot
+ using the new-style signal/slot scheme
Contents
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+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.
+
+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!"
+
+ ...
+
+ clicked = QtCore.Signal()
+
+ 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 QString and has
+ # 'saySomeWords' as its name
+ @QtCore.Slot(QtCore.QString)
+ def saySomeWords(words):
+ print words
+
+ class Communicate(QtCore.QObject):
+ # create a new signal on the fly and name it 'speak'
+ speak = QtCore.Signal(QtCore.QString)
+
+ 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 'QString'
+ # and has 'saySomething' as its name
+ @QtCore.Slot(int)
+ @QtCore.Slot(QtCore.QString)
+ 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 QStrings
+ speakNumber = QtCore.Signal(int)
+ speakWord = QtCore.Signal(QtCore.QString)
+
+ 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 'QString'
+ # and has 'saySomething' as its name
+ @QtCore.Slot(int)
+ @QtCore.Slot(QtCore.QString)
+ 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 QStrings
+ speak = QtCore.Signal((int,), (QtCore.QString,))
+
+ someone = Communicate()
+ # connect signal and slot. As 'int' is the default
+ # we have to inform the QString when connecting the
+ # second signal
+ someone.speak.connect(saySomething)
+ someone.speak[QtCore.QString].connect(saySomething)
+
+ # emit 'speak' signal with different arguments.
+ # we have to inform the QString as int is the default
+ someone.speak.emit(10)
+ someone.speak[QtCore.QString].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.