According to documentation of numpy.reshape, it returns a new array object with the new shape specified by the parameters (given that, with the new shape, the amount of elements in the array remain unchanged), without changing the shape of the original object, so when you are calling the. 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. The connect method has a non python-friendly syntax.

Qt allows us to connect multiple signals to the samesignal or slot. This can be useful when weprovide the user with many ways of performing the same operation.Sometimes, however, we would like the slot to behave slightlydifferently depending on which widget invoked it. In this article weexplore various solutions, including the use of QSignalMapper.

To illustrate the problem, we will implement a Keypad widget thatprovides ten QPushButtons, numbered 0 to 9, and adigitClicked(int) signal that is emitted when the user clicks abutton. We will review four solutions and discuss their respectivemerits.

The most straightforward solution to our problem (but also thesilliest) is to connect the ten QPushButton objects'clicked() signals to ten distinct slots calledbutton0Clicked() to button9Clicked(), each of which emits thedigitClicked(int) signal with a different parameter value (0 to9). Here's the definition of the Keypad class:

This is the Keypad constructor:

In the constructor, we create the QPushButtons, and we tediouslyconnect each button's clicked() signal to the correspondingprivate slot.

Each slot simply emits the digitClicked(int) signal with adifferent hard-coded argument.

Needless to say, this approach is inflexible and error-prone. It ispracticable for a small number of connections, but even for a10-key Keypad, the copy/paste is almost unbearable. Let's moveon to a better solution.

The next step is to merge thebuttonNClicked() slots into one private slotthat emits the digitClicked(int) signal with the correctparameter, depending on which button was clicked. This is possibleusing the QObject::sender() function, aswe will see shortly. The Keypad constructor becomes:

And this is the code for the buttonClicked() slot:

We start by calling sender() to retrieve a pointer to the QObjectthat emitted the signal that invoked this slot. In this particularexample, we know that the sender is a QPushButton, so we can castsender()'s return value to a QPushButton*. Then we emitthe digitClicked(int) signal with the digit value shown on thebutton.

The drawback of this approach is that we need a private slot to dothe demultiplexing. The code in buttonClicked() isn't veryelegant; if you suddenly replace the QPushButtons with anothertype of widget and forget to change the cast, you will get a crash.Similarly, if you change the text on the buttons (for example, 'NIL'instead of '0'), the digitClicked(int) signal will be emittedwith an incorrect value.

Finally, the use of sender() leads to tightly coupled components,which many people consider to be bad programming style. It isn't quiteso bad in this example, because Keypad already knows about thebutton objects, but if buttonClicked() was a slot in anotherclass, the use of sender() would have the unfortunate effect oftying that class to an implementation detail of the Keypad class.

Our third approach requires no private slot in Keypad; instead,we make sure that the buttons themselves emit a clicked(int)signal that can be directly connected to Keypad'sdigitClicked(int) signal. (When connecting a signal to anothersignal, the target signal is emitted whenever the first signal isemitted.) This requires subclassing QPushButton as follows:

Whenever QPushButton emits the clicked() signal, we interceptit in our KeypadButton subclass and emit the clicked(int)signal with the correct digit as the argument.

The Keypad constructor then looks like this:

This approach is both flexible and clean, but it is quite cumbersometo write, because it forces us to subclass QPushButton.

The fourth and last approach does not require any private slots,nor does it need a QPushButton subclass. Instead, the entiresignal-related logic is implemented in the Keypad class'sconstructor:

First, we create a QSignalMapper object. QSignalMapperinherits from QObject and provides a means of establishing arelationship between a set of zero-parameter signals and aone-parameter signal or slot. The call to setMapping() inside thefor loop establishes a mapping between a button and an integervalue; for example, buttons[3] is associated with the integervalue 3.

When the clicked() signal of a button is emitted,QSignalMapper's map() slot is invoked (thanks to theconnect() call in the for loop). If a mapping exists for theobject that emitted the signal, the mapped(int) signal is emittedwith the integer value set using setMapping(). That signal is inturn connected to the Keypad's digitClicked(int) signal.The setMapping() function exists in two versions: one that takesan int and one that takes a QString as the second argument.This makes it possible to associate an arbitrary string with a senderobject, instead of an integer. When such a mapping exists,QSignalMapper emits a mapped(const QString &) signal.

QSignalMapper does not directly support any other data types. Thismeans that, for example, if you were to implement a palette toolallowing the user to choose a color from a set of standard colors andneeded to emit a colorSelected(const QColor &) signal, your bestbet would be to use the sender() approach or the subclass approachdescribed above. If you already use a subclass of, say,QToolButton to represent a color, it doesn't cost you much to adda clicked(const QColor &) slot to it.

Signals And Slots Pyqt Array Java

last modified July 16, 2020

In this part of the PyQt5 programming tutorial, we explore events and signalsoccurring in applications.

Events in PyQt5

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GUI applications are event-driven. Events are generated mainly by theuser of an application. But they can be generated by other means as well; e.g. anInternet connection, a window manager, or a timer.When we call the application's exec_() method, the application entersthe main loop. The main loop fetches events and sends them to the objects.

In the event model, there are three participants:

• event source
• event object
• event target

The event source is the object whose state changes. It generates events.The event object (event) encapsulates the state changes in the event source.The event target is the object that wants to be notified. Event source objectdelegates the task of handling an event to the event target.

PyQt5 has a unique signal and slot mechanism to deal with events.Signals and slots are used for communication between objects. A signalis emitted when a particular event occurs. A slot can be any Python callable.A slot is called when its connected signal is emitted.

PyQt5 signals and slots

This is a simple example demonstrating signals and slots in PyQt5.

In our example, we display a QtGui.QLCDNumberand a QtGui.QSlider. We change the lcdnumber by dragging the slider knob.

Here we connect a valueChanged signal of the slider to thedisplay slot of the lcd number.

The sender is an object that sends a signal. The receiveris the object that receives the signal. The slot is the method thatreacts to the signal.

PyQt5 reimplementing event handler

Events in PyQt5 are processed often by reimplementing event handlers.

In our example, we reimplement the keyPressEvent() event handler.

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If we click the Escape button, the application terminates.

Event object in PyQt5

Event object is a Python object that contains a number of attributesdescribing the event. Event object is specific to the generated eventtype.

In this example, we display the x and ycoordinates of a mouse pointer in a label widget.

The x and y coordinates are displayd in a QLabelwidget.

Mouse tracking is disabled by default, so the widget only receives mouse moveevents when at least one mouse button is pressed while the mouse is being moved.If mouse tracking is enabled, the widget receives mouse move events evenif no buttons are pressed.

The e is the event object; it contains data about the eventthat was triggered; in our case, a mouse move event. With the x()and y() methods we determine the x and y coordinates ofthe mouse pointer. We build the string and set it to the label widget.

PyQt5 event sender

Sometimes it is convenient to know which widget is the sender of a signal.For this, PyQt5 has the sender method.

We have two buttons in our example. In the buttonClicked methodwe determine which button we have clicked by calling thesender() method.

Both buttons are connected to the same slot.

Signals And Slots Pyqt Array Tutorial

We determine the signal source by calling the sender() method.In the statusbar of the application, we show the labelof the button being pressed.

PyQt5 emitting signals

Objects created from a QObject can emit signals.The following example shows how we to emit custom signals.

We create a new signal called closeApp. This signal isemitted during a mouse press event. The signal is connected to theclose() slot of the QMainWindow.

A signal is created with the pyqtSignal() as a class attributeof the external Communicate class.

The custom closeApp signal is connected to the close()slot of the QMainWindow.

When we click on the window with a mouse pointer, the closeApp signalis emitted. The application terminates.

In this part of the PyQt5 tutorial, we have covered signals and slots.