PySide/PyQt truncate text in QLabel based on minimumSize - qt

Question

I am wondering how to best truncate text in a QLabel based on it's maximum width/height.
The incoming text could be any length, but in order to keep a tidy layout I'd like to truncate long strings to fill a maximum amount of space (widget's maximum width/height).
E.g.:
'A very long string where there should only be a short one, but I can't control input to the widget as it's a user given value'
would become:
'A very long string where there should only be a short one, but ...'
based on the required space the current font needs.
How can I achieve this best?
Here is a simple example of what I'm after, though this is based on word count, not available space:
import sys
from PySide.QtGui import *
from PySide.QtCore import *
def truncateText(text):
maxWords = 10
words = text.split(' ')
return ' '.join(words[:maxWords]) + ' ...'
app = QApplication(sys.argv)
mainWindow = QWidget()
layout = QHBoxLayout()
mainWindow.setLayout(layout)
text = 'this is a very long string, '*10
label = QLabel(truncateText(text))
label.setWordWrap(True)
label.setFixedWidth(200)
layout.addWidget(label)
mainWindow.show()
sys.exit(app.exec_())

Answer 1

Even easier - use the QFontMetrics.elidedText method and overload the paintEvent, here's an example:
from PyQt4.QtCore import Qt
from PyQt4.QtGui import QApplication,\
QLabel,\
QFontMetrics,\
QPainter
class MyLabel(QLabel):
def paintEvent( self, event ):
painter = QPainter(self)
metrics = QFontMetrics(self.font())
elided = metrics.elidedText(self.text(), Qt.ElideRight, self.width())
painter.drawText(self.rect(), self.alignment(), elided)
if ( __name__ == '__main__' ):
app = None
if ( not QApplication.instance() ):
app = QApplication([])
label = MyLabel()
label.setText('This is a really, long and poorly formatted runon sentence used to illustrate a point')
label.setWindowFlags(Qt.Dialog)
label.show()
if ( app ):
app.exec_()

Answer 2

I found that #Eric Hulser's answer, while great, didn't work when the label was put into another widget.
I came up with this by hacking together Eric's response with the Qt Elided Label Example. It should behave just like a regular label, yet elide horizontally when the text width exceeds the widget width. It has an extra argument for different elide modes. I also wrote some tests for fun :)
If you want to use PyQt5...
Change "PySide2" to "PyQt5"
Change "Signal" to "pyqtSignal"
Enjoy!
Eliding Label
# eliding_label.py
from PySide2 import QtCore, QtWidgets, QtGui
class ElidingLabel(QtWidgets.QLabel):
"""Label with text elision.
QLabel which will elide text too long to fit the widget. Based on:
https://doc-snapshots.qt.io/qtforpython-5.15/overviews/qtwidgets-widgets-elidedlabel-example.html
Parameters
----------
text : str
Label text.
mode : QtCore.Qt.TextElideMode
Specify where ellipsis should appear when displaying texts that
don’t fit.
Default is QtCore.Qt.ElideMiddle.
Possible modes:
QtCore.Qt.ElideLeft
QtCore.Qt.ElideMiddle
QtCore.Qt.ElideRight
parent : QWidget
Parent widget. Default is None.
f : Qt.WindowFlags()
https://doc-snapshots.qt.io/qtforpython-5.15/PySide2/QtCore/Qt.html#PySide2.QtCore.PySide2.QtCore.Qt.WindowType
"""
elision_changed = QtCore.Signal(bool)
def __init__(self, text='', mode=QtCore.Qt.ElideMiddle, **kwargs):
super().__init__(**kwargs)
self._mode = mode
self.is_elided = False
self.setSizePolicy(QtWidgets.QSizePolicy.Expanding, QtWidgets.QSizePolicy.Preferred)
self.setText(text)
def setText(self, text):
self._contents = text
# This line set for testing. Its value is the return value of
# QFontMetrics.elidedText, set in paintEvent. The variable
# must be initialized for testing. The value should always be
# the same as contents when not elided.
self._elided_line = text
self.update()
def text(self):
return self._contents
def paintEvent(self, event):
super().paintEvent(event)
did_elide = False
painter = QtGui.QPainter(self)
font_metrics = painter.fontMetrics()
text_width = font_metrics.horizontalAdvance(self.text())
# layout phase
text_layout = QtGui.QTextLayout(self._contents, painter.font())
text_layout.beginLayout()
while True:
line = text_layout.createLine()
if not line.isValid():
break
line.setLineWidth(self.width())
if text_width >= self.width():
self._elided_line = font_metrics.elidedText(self._contents, self._mode, self.width())
painter.drawText(QtCore.QPoint(0, font_metrics.ascent()), self._elided_line)
did_elide = line.isValid()
break
else:
line.draw(painter, QtCore.QPoint(0, 0))
text_layout.endLayout()
if did_elide != self.is_elided:
self.is_elided = did_elide
self.elision_changed.emit(did_elide)
if __name__ == '__main__':
app = QtWidgets.QApplication([])
long_text = "this is some long text, wouldn't you say?"
elabel = ElidingLabel(long_text)
elabel.show()
app.exec_()
Test Eliding Label
# test_eliding_label.py.py
#
# Run tests with
#
# python3 -m unittest test_eliding_label.py --failfast --quiet
import unittest
import unittest.mock
from PySide2 import QtCore, QtWidgets, QtGui, QtTest
import eliding_label
if not QtWidgets.QApplication.instance():
APP = QtWidgets.QApplication([]) # pragma: no cover
class TestElidingLabelArguments(unittest.TestCase):
def test_optional_text_argument(self):
elabel = eliding_label.ElidingLabel()
self.assertEqual(elabel.text(), "")
def test_text_argument_sets_label_text(self):
elabel = eliding_label.ElidingLabel(text="Test text")
self.assertEqual(elabel.text(), "Test text")
def test_optional_elision_mode_argument(self):
elabel = eliding_label.ElidingLabel()
self.assertEqual(elabel._mode, QtCore.Qt.ElideMiddle)
class TestElidingLabel(unittest.TestCase):
def setUp(self):
self.elabel = eliding_label.ElidingLabel()
def test_elabel_is_a_label(self):
self.assertIsInstance(self.elabel, QtWidgets.QLabel)
def test_has_elision_predicate(self):
self.assertEqual(self.elabel.is_elided, False)
def test_elision_predicate_changes_when_text_width_exceeds_widget_width(self):
# NOTE: This is a bit of a stretch, inducing a paint event
# when the event loop isn't running. Throws a bunch of C++
# sourced text which can't be (easily) caught.
self.elabel.setFixedWidth(25)
self.assertEqual(self.elabel.width(), 25)
long_text = "This is line is definely longer than 25 pixels."
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
long_text_width = font_metrics.horizontalAdvance(long_text)
self.assertGreater(long_text_width, 25)
self.elabel.setText(long_text)
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
self.assertEqual(self.elabel.is_elided, True)
def test_text_is_elided_when_text_width_exceeds_widget_width(self):
# NOTE: This is a bit of a stretch, inducing a paint event
# when the event loop isn't running. Throws a bunch of C++
# sourced text which can't be (easily) caught.
self.elabel.setFixedWidth(25)
self.assertEqual(self.elabel.width(), 25)
long_text = "This is line is definely longer than 25 pixels."
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
long_text_width = font_metrics.horizontalAdvance(long_text)
self.assertGreater(long_text_width, 25)
self.elabel.setText(long_text)
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
# PySide2.QtGui.QFontMetrics.elidedText states, "If the string
# text is wider than width , returns an elided version of the
# string (i.e., a string with '…' in it). Otherwise, returns
# the original string."
self.assertEqual(self.elabel._elided_line, '…')
def test_text_is_not_elided_when_text_width_is_less_than_widget_width(self):
# NOTE: This is a bit of a stretch, inducing a paint event
# when the event loop isn't running. Throws a bunch of C++
# sourced text which can't be (easily) caught.
self.elabel.setFixedWidth(500)
self.assertEqual(self.elabel.width(), 500)
short_text = "Less than 500"
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
short_text_width = font_metrics.horizontalAdvance(short_text)
self.assertLess(short_text_width, 500)
self.elabel.setText(short_text)
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
# PySide2.QtGui.QFontMetrics.elidedText states, "If the string
# text is wider than width , returns an elided version of the
# string (i.e., a string with '…' in it). Otherwise, returns
# the original string."
self.assertEqual(self.elabel._elided_line, short_text)
def test_stores_full_text_even_when_elided(self):
# NOTE: This is a bit of a stretch, inducing a paint event
# when the event loop isn't running. Throws a bunch of C++
# sourced text which can't be (easily) caught.
self.elabel.setFixedWidth(25)
self.assertEqual(self.elabel.width(), 25)
long_text = "This is line is definely longer than 25 pixels."
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
long_text_width = font_metrics.horizontalAdvance(long_text)
self.assertGreater(long_text_width, 25)
self.elabel.setText(long_text)
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
# PySide2.QtGui.QFontMetrics.elidedText states, "If the string
# text is wider than width , returns an elided version of the
# string (i.e., a string with '…' in it). Otherwise, returns
# the original string."
self.assertEqual(self.elabel._elided_line, '…')
self.assertEqual(self.elabel.text(), long_text)
def test_has_elision_changed_signal(self):
self.assertIsInstance(self.elabel.elision_changed, QtCore.Signal)
def test_elision_changed_signal_emits_on_change_to_is_elided_predicate(self):
mock = unittest.mock.Mock()
self.elabel.elision_changed.connect(mock.method)
# NOTE: This is a bit of a stretch, inducing a paint event
# when the event loop isn't running. Throws a bunch of C++
# sourced text which can't be (easily) caught.
# Induce elision
self.elabel.setFixedWidth(150)
self.assertEqual(self.elabel.width(), 150)
long_text = "This line is definitely going to be more than 150 pixels"
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
long_text_width = font_metrics.horizontalAdvance(long_text)
self.assertGreater(long_text_width, 150)
self.elabel.setText(long_text)
self.assertEqual(self.elabel.is_elided, False) # no elide until painting
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
self.assertEqual(self.elabel.is_elided, True)
mock.method.assert_called_once()
# Remove elision
short_text = "Less than 150"
painter = QtGui.QPainter()
font_metrics = painter.fontMetrics()
short_text_width = font_metrics.horizontalAdvance(short_text)
self.assertLess(short_text_width, 150)
self.elabel.setText(short_text)
self.assertEqual(self.elabel.is_elided, True) # still elided until painting
x = self.elabel.x()
y = self.elabel.y()
w = self.elabel.width()
h = self.elabel.height()
paint_event = QtGui.QPaintEvent(QtGui.QRegion(x, y, w, h))
self.elabel.paintEvent(paint_event)
self.assertEqual(self.elabel.is_elided, False)
self.assertEqual(mock.method.call_count, 2)

Answer 3

You can achieves this through determining the width with QFontMetrics, see this answer.
You would probably want to use or create some algorithm which finds the place to cut quickly, unless doing it in a simple for loop would be sufficient.

Answer 4

simpler solution if you want show QLabel in center in provided area
label.setAlignment(Qt.AlignmentFlag.AlignCenter)
label.minimumSizeHint = lambda self=label: QSize(0, QLabel.minimumSizeHint(self).height() )