QObject::connect(const QObject.sender, PointerToMemberFunction signal, Functor method) The first one is the one that is much closer to the old syntax: you connect a signal from the sender to a slot in a receiver object. The two other overloads are connecting a signal to a static function or a functor object without a receiver. Ignore signal (SIGIGN): The signal is ignored and the code execution will continue even if not meaningful. Function handler: A specific function is defined to handle the signal. Either SIGDFL or SIGIGN is set as the default signal handling behavior at program startup for each of the supported signals.

1. C++ Signal Slot
2. C Signal Sigusr1

• PyQt Tutorial

1. Signal and Slot Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks. In GUI programming, when we change one widget, we often want another widget to be notified.
2. Signals and slots are used for communication between objects. The signals and slots mechanism is a central feature of Qt and probably the part that differs most from the features provided by other frameworks. Signals and slots are made possible by Qt's meta-object system.

• PyQt Useful Resources

• Selected Reading

Unlike a console mode application, which is executed in a sequential manner, a GUI based application is event driven. Functions or methods are executed in response to user’s actions like clicking on a button, selecting an item from a collection or a mouse click etc., called events.

Widgets used to build the GUI interface act as the source of such events. Each PyQt widget, which is derived from QObject class, is designed to emit ‘signal’ in response to one or more events. The signal on its own does not perform any action. Instead, it is ‘connected’ to a ‘slot’. The slot can be any callable Python function.

In PyQt, connection between a signal and a slot can be achieved in different ways. Following are most commonly used techniques −

A more convenient way to call a slot_function, when a signal is emitted by a widget is as follows −

Suppose if a function is to be called when a button is clicked. Here, the clicked signal is to be connected to a callable function. It can be achieved in any of the following two techniques −

or

Example

In the following example, two QPushButton objects (b1 and b2) are added in QDialog window. We want to call functions b1_clicked() and b2_clicked() on clicking b1 and b2 respectively.

When b1 is clicked, the clicked() signal is connected to b1_clicked() function

When b2 is clicked, the clicked() signal is connected to b2_clicked() function

C++ Signal Slot

Example

C Signal Sigusr1

The above code produces the following output −

Output