In Qt (and most User Interfaces) ‘widget’ is the name given to a component of the UI that the user can interact with. User interfaces are made up of multiple widgets, arranged within the window.
Qt comes with a large selection of widgets available, and even allows you to create your own custom and customized widgets.
A quick demo
First let's have a look at some of the most common PyQt widgets. The following code creates a range of PyQt widgets and adds them to a window layout so you can see them together.
We'll cover how layouts work in Qt in the next tutorial.
import sys from PyQt5.QtCore import Qt from PyQt5.QtWidgets import ( QApplication, QCheckBox, QComboBox, QDateEdit, QDateTimeEdit, QDial, QDoubleSpinBox, QFontComboBox, QLabel, QLCDNumber, QLineEdit, QMainWindow, QProgressBar, QPushButton, QRadioButton, QSlider, QSpinBox, QTimeEdit, QVBoxLayout, QWidget, ) # Subclass QMainWindow to customize your application's main window class MainWindow(QMainWindow): def __init__(self): super().__init__() self.setWindowTitle("Widgets App") layout = QVBoxLayout() widgets = [ QCheckBox, QComboBox, QDateEdit, QDateTimeEdit, QDial, QDoubleSpinBox, QFontComboBox, QLCDNumber, QLabel, QLineEdit, QProgressBar, QPushButton, QRadioButton, QSlider, QSpinBox, QTimeEdit, ] for w in widgets: layout.addWidget(w()) widget = QWidget() widget.setLayout(layout) # Set the central widget of the Window. Widget will expand # to take up all the space in the window by default. self.setCentralWidget(widget) app = QApplication(sys.argv) window = MainWindow() window.show() app.exec()
Run it! You'll see a window appear containing all the widgets we've created.
Big ol' list of widgets on Windows, Mac & Ubuntu Linux.
Lets have a look at all the example widgets, from top to bottom:
|Widget||What it does|
||A dropdown list box|
||For editing dates and datetimes|
||For editing dates and datetimes|
||A number spinner for floats|
||A list of fonts|
||A quite ugly LCD display|
||Just a label, not interactive|
||Enter a line of text|
||A progress bar|
||A toggle set, with only one active item|
||An integer spinner|
||For editing times|
There are far more widgets than this, but they don’t fit so well! You can see them all by checking the Qt documentation.
Next, we'll step through some of the most commonly used widgets and look at them in more detail. To experiment with the widgets we'll need a simple application to put them in. Save the following code to a file named
app.py and run it to make sure it's working.
import sys from PyQt5.QtWidgets import ( QMainWindow, QApplication, QLabel, QCheckBox, QComboBox, QListWidget, QLineEdit, QLineEdit, QSpinBox, QDoubleSpinBox, QSlider ) from PyQt5.QtCore import Qt class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") app = QApplication(sys.argv) w = MainWindow() w.show() app.exec()
In the code above we've imported a number of Qt widgets. Now we'll step through each of those widgets in turn, adding them to our application and seeing how they behave.
We'll start the tour with
QLabel, arguably one of the simplest widgets available in the Qt toolbox. This is a simple one-line piece of text that you can position in your application. You can set the text by passing in a
str as you create it:
widget = QLabel("Hello")
Or, by using the
widget = QLabel("1") # The label is created with the text 1. widget.setText("2") # The label now shows 2.
You can also adjust font parameters, such as the size of the font or the alignment of text in the widget.
class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") widget = QLabel("Hello") font = widget.font() font.setPointSize(30) widget.setFont(font) widget.setAlignment(Qt.AlignHCenter | Qt.AlignVCenter) self.setCentralWidget(widget)
QLabel on Windows, Mac & Ubuntu Linux.
Font tip Note that if you want to change the properties of a widget font it is usually better to get the current font, update it and then apply it back. This ensures the font face remains in keeping with the desktop conventions.
The alignment is specified by using a flag from the
The flags available for horizontal alignment are:
||Aligns with the left edge.|
||Aligns with the right edge.|
||Centers horizontally in the available space.|
||Justifies the text in the available space.|
The flags available for vertical alignment are:
||Aligns with the top.|
||Aligns with the bottom.|
||Centers vertically in the available space.|
You can combine flags together using pipes (
|), however note that you
can only use vertical or horizontal alignment flag at a time.
align_top_left = Qt.AlignLeft | Qt.AlignTop
Note that you use an OR pipe (`|`) to combine the two flags (not
A & B). This is because the flags are non-overlapping bitmasks. e.g.
Qt.AlignmentFlag.AlignLeft has the hexadecimal value
0x0040. By ORing together we get the value
0x0041 representing 'bottom left'. This principle applies to all other combinatorial Qt flags. If this is gibberish to you, feel free to ignore and move on. Just remember to use |
Finally, there is also a shorthand flag that centers in both directions simultaneously:
||Centers horizontally and vertically|
Weirdly, you can also use
QLabel to display an image using
.setPixmap(). This accepts an pixmap, which you can create by passing an image filename to
QPixmap. In the example files provided with this book you can find a file
otje.jpg which you can display in your window as follows:
"Otje" the cat.
What a lovely face. By default the image scales while maintaining its aspect ratio. If you want it to stretch and scale to fit the window completely you can set
.setScaledContents(True) on the
The next widget to look at is
QCheckBox() which, as the name suggests, presents a checkable box to the user. However, as with all Qt widgets there are number of configurable options to change the widget behaviors.
class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") widget = QCheckBox() widget.setCheckState(Qt.Checked) # For tristate: widget.setCheckState(Qt.PartiallyChecked) # Or: widget.setTriState(True) widget.stateChanged.connect(self.show_state) self.setCentralWidget(widget) def show_state(self, s): print(s == Qt.Checked) print(s)
QCheckBox on Windows, Mac & Ubuntu Linux.
You can set a checkbox state programmatically using
.setCheckState. The former accepts either
False representing checked or unchecked respectively. However, with
.setCheckState you also specify a particular checked state using a
Qt. namespace flag:
||Item is unchecked|
||Item is partially checked|
||Item is checked|
A checkbox that supports a partially-checked (
Qt.PartiallyChecked) state is commonly referred to as 'tri-state', that is being neither on nor off. A checkbox in this state is commonly shown as a greyed out checkbox, and is commonly used in hierarchical checkbox arrangements where sub-items are linked to parent checkboxes.
If you set the value to
Qt.PartiallyChecked the checkbox will become tristate. You can also set a checkbox to be tri-state without setting the current state to partially checked by using
You may notice that when the script is running the current state number is displayed as an
int with checked =
2, unchecked =
0, and partially checked =
1. You don’t need to remember these values, the
Qt.Checked namespace variable
== 2 for example. This is the value of these state's respective flags. This means you can test state using
state == Qt.Checked.
QComboBox is a drop down list, closed by default with an arrow to open it. You can select a single item from the list, with the currently selected item being shown as a label on the widget. The combo box is suited to selection of a choice from a long list of options.
You have probably seen the combo box used for selection of font faces, or size, in word processing applications. Although Qt actually provides a specific font-selection combo box as
You can add items to a
QComboBox by passing a list of strings to
.addItems(). Items will be added in the order they are provided.
class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") widget = QComboBox() widget.addItems(["One", "Two", "Three"]) # Sends the current index (position) of the selected item. widget.currentIndexChanged.connect( self.index_changed ) # There is an alternate signal to send the text. widget.currentTextChanged.connect( self.text_changed ) self.setCentralWidget(widget) def index_changed(self, i): # i is an int print(i) def text_changed(self, s): # s is a str print(s)
QComboBox on Windows, Mac & Ubuntu Linux.
.currentIndexChanged signal is triggered when the currently selected item is updated, by default passing the index of the selected item in the list.
There is also a
.currentTextChanged signal which instead provides the label of the currently selected item, which is often more useful.
QComboBox can also be editable, allowing users to enter values not currently in the list and either have them inserted, or simply used as a value. To make the box editable:
You can also set a flag to determine how the insert is handled. These flags are stored on the
QComboBox class itself and are listed below:
||Insert as first item|
||Replace currently selected item|
||Insert after last item|
||Insert after current item|
||Insert before current item|
||Insert in alphabetical order|
To use these, apply the flag as follows:
You can also limit the number of items allowed in the box by using
For a more in-depth look at the
QComboBox take a look at my QComboBox documentation.
This widget is similar to
QComboBox, except options are presented as a scrollable list of items. It also supports selection of multiple items at once. A
QListWidget offers an
currentItemChanged signal which sends the
QListWidgetItem (the element of the list widget), and a
currentTextChanged signal which sends the text of the current item.
class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") widget = QListWidget() widget.addItems(["One", "Two", "Three"]) widget.currentItemChanged.connect(self.index_changed) widget.currentTextChanged.connect(self.text_changed) self.setCentralWidget(widget) def index_changed(self, i): # Not an index, i is a QListWidgetItem print(i.text()) def text_changed(self, s): # s is a str print(s)
QListWidget on Windows, Mac & Ubuntu Linux.
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QLineEdit widget is a simple single-line text editing box, into which users can type input. These are used for form fields, or settings where there is no restricted list of valid inputs. For example, when entering an email address, or computer name.
class MainWindow(QMainWindow): def __init__(self): super(MainWindow, self).__init__() self.setWindowTitle("My App") widget = QLineEdit() widget.setMaxLength(10) widget.setPlaceholderText("Enter your text") #widget.setReadOnly(True) # uncomment this to make readonly widget.returnPressed.connect(self.return_pressed) widget.selectionChanged.connect(self.selection_changed) widget.textChanged.connect(self.text_changed) widget.textEdited.connect(self.text_edited) self.setCentralWidget(widget) def return_pressed(self): print("Return pressed!") self.centralWidget().setText("BOOM!") def selection_changed(self): print("Selection changed") print(self.centralWidget().selectedText()) def text_changed(self, s): print("Text changed...") print(s) def text_edited(self, s): print("Text edited...") print(s)
QLineEdit on Windows, Mac & Ubuntu Linux.
As demonstrated in the above code, you can set a maximum length for the text in a line edit.
QLineEdit has a number of signals available for different editing events including when return is pressed (by the user), when the user selection is changed. There are also two edit signals, one for when the text in the box has been edited and one for when it has been changed. The distinction here is between user edits and programmatic changes. The
textEdited signal is only sent when the user edits text.
Additionally, it is possible to perform input validation using an input mask to define which characters are supported and where. This can be applied to the field as follows:
The above would allow a series of 3-digit numbers separated with periods, and could therefore be used to validate IPv4 addresses.
QSpinBox and QDoubleSpinBox
QSpinBox provides a small numerical input box with arrows to increase and decrease the value.
QSpinBox supports integers while the related widget
QDoubleSpinBox supports floats.
class MainWindow(QMainWindow): def __init__(self): super().__init__() self.setWindowTitle("My App") widget = QSpinBox() # Or: widget = QDoubleSpinBox() widget.setMinimum(-10) widget.setMaximum(3) # Or: widget.setRange(-10,3) widget.setPrefix("$") widget.setSuffix("c") widget.setSingleStep(3) # Or e.g. 0.5 for QDoubleSpinBox widget.valueChanged.connect(self.value_changed) widget.textChanged.connect(self.value_changed_str) self.setCentralWidget(widget) def value_changed(self, i): print(i) def value_changed_str(self, s): print(s)
Run it and you'll see a numeric entry box. The value shows pre and post fix units, and is limited to the range +3 to -10.
QSpinBox on Windows, Mac & Ubuntu Linux.
The demonstration code above shows the various features that are available for the widget.
To set the range of acceptable values you can use
setMaximum, or alternatively use
setRange to set both simultaneously. Annotation of value types is supported with both prefixes and suffixes that can be added to the number, e.g. for currency markers or units using
Clicking on the up and down arrows on the widget will increase or decrease the value in the widget by an amount, which can be set using
.setSingleStep. Note that this has no effect on the values that are acceptable to the widget.
QDoubleSpinBox have a
.valueChanged signal which fires whenever their value is altered. The raw
.valueChanged signal sends the numeric value (either an
int or a
.textChanged sends the value as a string, including both the prefix and suffix characters.
You can optionally disable text input on the spin box line edit, by setting it to read-only. With this set, the value can only by changed using the controls. This also has the side effect of disabling the flashing cursor.
QSlider provides a slide-bar widget, which functions internally much like a
QDoubleSpinBox. Rather than display the current value numerically, it is represented by the position of the slider handle along the length of the widget. This is often useful when providing adjustment between two extremes, but where absolute accuracy is not required. The most common use of this type of widget is for volume controls.
There is an additional
.sliderMoved signal that is triggered whenever the slider moves position and a
.sliderPressed signal that emits whenever the slider is clicked.
class MainWindow(QMainWindow): def __init__(self): super().__init__() self.setWindowTitle("My App") widget = QSlider() widget.setMinimum(-10) widget.setMaximum(3) # Or: widget.setRange(-10,3) widget.setSingleStep(3) widget.valueChanged.connect(self.value_changed) widget.sliderMoved.connect(self.slider_position) widget.sliderPressed.connect(self.slider_pressed) widget.sliderReleased.connect(self.slider_released) self.setCentralWidget(widget) def value_changed(self, i): print(i) def slider_position(self, p): print("position", p) def slider_pressed(self): print("Pressed!") def slider_released(self): print("Released")
Run this and you'll see a slider widget. Drag the slider to change the value.
QSlider on Windows, Mac & Ubuntu Linux.
You can also construct a slider with a vertical or horizontal orientation by passing the orientation in as you create it. The orientation flags are defined in the
Qt. namespace. For example --
widget = QSlider(Qt.Vertical)
widget = QSlider(Qt.Horizontal)
QDial is a rotatable widget that functions just like the slider, but appears as an analogue dial. This looks nice, but from a UI perspective is not particularly user friendly. However, they are often used in audio applications as representation of real-world analogue dials.
class MainWindow(QMainWindow): def __init__(self): super().__init__() self.setWindowTitle("My App") widget = QDial() widget.setRange(-10, 100) widget.setSingleStep(0.5) widget.valueChanged.connect(self.value_changed) widget.sliderMoved.connect(self.slider_position) widget.sliderPressed.connect(self.slider_pressed) widget.sliderReleased.connect(self.slider_released) self.setCentralWidget(widget) def value_changed(self, i): print(i) def slider_position(self, p): print("position", p) def slider_pressed(self): print("Pressed!") def slider_released(self): print("Released")
Run this and you'll see a circular dial, rotate it to select a number from the range.
QDial on Windows, Mac & Ubuntu Linux.
The signals are the same as for
QSlider and retain the same names (e.g.
This concludes our brief tour of the common widgets used in PyQt applications. To see the full list of available widgets, including all their signals and attributes, take a look at the Qt documentation.