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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. PySide uses `PSEP100 <http://www.pyside.org/docs/pseps/psep-0100.html>`_ 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.
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