Graphical applications (GUI) are event-driven, unlike console or terminal applications. A users action like clicks a button or selecting an item in a list is called an event.
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If an event takes place, each PyQt5 widget can emit a signal. A signal does not execute any action, that is done by a slot.
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Related course:
Create GUI Apps with PyQt5
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Signals and slot introduction
Consider this example:
The button click (signal) is connected to the action (slot). In this example, the method slot_method will be called if the signal emits.
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Stringdata and data are initialized with some data explained later in this article. Staticmetacall is a function pointer initialized to Counter::qtstaticmetacall. Introspection Tables. First, let us analyze the integer data of QMetaObject. To break it down: slots add a data descriptor to the class that points to a slot in a struct-like datastructure. They get accessed pretty fast, and they take much less space than even the new smaller dict (like a tuple amount of space). It should be easy to programmatically determine if they should be added in the child or not.
If a class defines a slot also defined in a base class, the instance variable defined by the base class slot is inaccessible (except by retrieving its descriptor directly from the base class). This renders the meaning of the program undefined. In the future, a check may be added to prevent this. Traditional syntax: SIGNAL and SLOT QtCore.SIGNAL and QtCore.SLOT macros allow Python to interface with Qt signal and slot delivery mechanisms. This is the old way of using signals and slots. The example below uses the well known clicked signal from a QPushButton. With the addition of PEP 526, Python has a concise way to specify the type of class members. This PEP leverages that syntax to provide a simple, unobtrusive way to describe Data Classes. With two exceptions, the specified attribute type annotation is completely ignored by Data Classes. No base classes or metaclasses are used by Data Classes.
This principle of connecting slots methods or function to a widget, applies to all widgets,
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or we can explicitly define the signal:
PyQt supports many type of signals, not just clicks.
Example
We can create a method (slot) that is connected to a widget. A slot is any callable function or method.
On running the application, we can click the button to execute the action (slot).
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If you are new to programming Python PyQt, I highly recommend this book.