Qt Slot Call Order
The button click (signal) is connected to the action (slot). In this example, the method slotmethod will be called if the signal emits. This principle of connecting slots methods or function to a widget, applies to all widgets.
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.
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.
Related course:
Create GUI Apps with PyQt5
In Qt v4.5 and earlier: No, the order is undefined as can be seen in the documentation here: If several slots are connected to one signal, the slots will be executed one after the other, in an arbitrary order, when the signal is emitted. Edit: From version 4.6 onwards this is no longer true. Now the slots will run in the order they are connected. An overview of Qt’s signals and slots inter-object communication mechanism. 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. Qt uses a command line tool that parses these project files in order to generate 'makefiles', files that are used by compilers to build an application. This tool is called qmake. But, we shouldn't bother too much about qmake, since Qt Creator will do the job for us.
Signals and slot introduction
Consider this example:
Qt Slot Call Ordering
The button click (signal) is connected to the action (slot). In this example, the method slot_method will be called if the signal emits.
This principle of connecting slots methods or function to a widget, applies to all widgets,
or we can explicitly define the signal:
Qt Slot Call Orders
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).
If you are new to programming Python PyQt, I highly recommend this book.