Python Bindings for KDE (PyKDE-3.11)
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# Signal and Slot Support

## General Signals and Slots

A signal may be either a Qt signal (specified using `SIGNAL()`) or a Python signal (specified using `PYSIGNAL()`).

A slot can be either a Python callable object, a Qt signal (specified using `SIGNAL()`), a Python signal (specified using `PYSIGNAL()`), or a Qt slot (specified using `SLOT()`).

You connect signals to slots (and other signals) as you would from C++. For example:

    QObject.connect(a,SIGNAL("QtSig()"),pyFunction)
    QObject.connect(a,SIGNAL("QtSig()"),pyClass.pyMethod)
    QObject.connect(a,SIGNAL("QtSig()"),PYSIGNAL("PySig"))
    QObject.connect(a,SIGNAL("QtSig()"),SLOT("QtSlot()"))
    QObject.connect(a,PYSIGNAL("PySig"),pyFunction)
    QObject.connect(a,PYSIGNAL("PySig"),pyClass.pyMethod)
    QObject.connect(a,PYSIGNAL("PySig"),SIGNAL("QtSig()"))
    QObject.connect(a,PYSIGNAL("PySig"),SLOT("QtSlot()"))

When a slot is a Python method that corresponds to a Qt slot then a signal can be connected to either the Python method or the Qt slot. The following connections achieve the same effect.

    sbar = QScrollBar()
    lcd = QLCDNumber()

    QObject.connect(sbar,SIGNAL("valueChanged(int)"),lcd.display)
    QObject.connect(sbar,SIGNAL("valueChanged(int)"),lcd,SLOT("display(int)"))

The difference is that the second connection is made at the C++ level and is more efficient.

Disconnecting signals works in exactly the same way.

Any instance of a class that is derived from the `QObject` class can emit a signal using the `emit` method. This takes two arguments. The first is the Python or Qt signal, the second is a Python tuple which are the arguments to the signal. For example:

    a.emit(SIGNAL("clicked()"),())
    a.emit(PYSIGNAL("pySig"),("Hello","World"))

Qt allows a signal to be connected to a slot that requires fewer arguments than the signal passes. The extra arguments are quietly discarded. Python slots can be used in the same way.

## Slots in Menus, Toolbars and Actions

The C++ declarations for menu items or KActions are similar to these examples:

    int QMenuData::insertItem (const QString & text,
         const QObject * receiver, const char * member,
         int accel = 0, int id = -1, int index = -1 )

    KAction ( const QString& text, int accel,
         const QObject* receiver, const char* slot,
         QObject* parent, const char* name = 0 )

Notice the "const QObject* receiver, const char* slot" parameters for each declaration.

In PyKDE, these two parameters are replaced with a SINGLE parameter that specifies the slot to be connected to the menu item, toolbar button or KAction:

    p = insertItem ("Open", self.slotOpen, 0, -1, -1)

    action = KAction ("Open", 0, self.slotOpen, None, 0)

This substitution applies to appropriate methods in KStdAction, KAction and related subclasses, KAccelMenu and KToolBar

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