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Qt: Dead lock detected - Sender is QPushButton(), receiver is PyQtSlotProxy() - for specific indexes in a QPushButton list

I am new to pyqt, and I tried to make an application window that contains a list of buttons that are able to toggle a different window. Since I want the number of these buttons to be of a varying quantity, I created a list of QPushButton elements for iterating over them, creating as many as defined by the length of the list, nevertheless I noticed a very weird behavior :
The following code ...
import sys
from random import randint
from PyQt5 import QtWidgets
class AnotherWindow(QtWidgets.QWidget):
"""
This "window" is a QWidget. If it has no parent,
it will appear as a free-floating window.
"""
def __init__(self):
super().__init__()
layout = QtWidgets.QVBoxLayout()
self.label = QtWidgets.QLabel("Another Window % d" % randint(0, 100))
layout.addWidget(self.label)
self.setLayout(layout)
class MainWindow(QtWidgets.QMainWindow):
def __init__(self,windows):
super().__init__()
self.windows=[]
self.buttons=[]
l=QtWidgets.QVBoxLayout()
for i in range(len(windows)):
window=AnotherWindow()
self.windows.append(window)
button=QtWidgets.QPushButton(f'window {windows[i]}')
print(i," ",button)
self.buttons.append(button)
self.buttons[i].clicked.connect(self.toggle_window,i)
l.addWidget(self.buttons[i])
w = QtWidgets.QWidget()
w.setLayout(l)
self.setCentralWidget(w)
print(len(self.windows))
def toggle_window(self,i):
if self.windows[i].isVisible():
self.windows[i].hide()
else:
self.windows[i].show()
if __name__=="__main__":
app = QtWidgets.QApplication(sys.argv)
windows=[0,1,2,3]
windows=[str(i) for i in windows]
print(windows)
w = MainWindow(windows)
w.show()
app.exec()
produced the following error but only when the 4rth button (window 3) is pressed.
Qt: Dead lock detected while activating a BlockingQueuedConnection: Sender is QPushButton( ... ), receiver is PyQtSlotProxy( ... )
In effort to validate the code, I tried to narrow the list into a linear declaration of a static number of QPushButton instances, indicating that the issue occurs, only when I try to put the buttons on a list. For instance, the following script does not present any similar unpredictable behavior:
import sys
from random import randint
from PyQt5 import QtWidgets
class AnotherWindow(QtWidgets.QWidget):
"""
This "window" is a QWidget. If it has no parent,
it will appear as a free-floating window.
"""
def __init__(self):
super().__init__()
layout = QtWidgets.QVBoxLayout()
self.label = QtWidgets.QLabel("Another Window % d" % randint(0, 100))
layout.addWidget(self.label)
self.setLayout(layout)
class MainWindow(QtWidgets.QMainWindow):
def __init__(self):
super().__init__()
self.window0 = AnotherWindow()
self.window1 = AnotherWindow()
self.window2 = AnotherWindow()
self.window3 = AnotherWindow()
l = QtWidgets.QVBoxLayout()
button0 = QtWidgets.QPushButton("window 0")
button0.clicked.connect(self.toggle_window0)
l.addWidget(button0)
button1 = QtWidgets.QPushButton("window 1")
button1.clicked.connect(self.toggle_window1)
l.addWidget(button1)
button2 = QtWidgets.QPushButton("window 2")
button2.clicked.connect(self.toggle_window2)
l.addWidget(button2)
button3 = QtWidgets.QPushButton("window 3")
button3.clicked.connect(self.toggle_window3)
l.addWidget(button3)
w = QtWidgets.QWidget()
w.setLayout(l)
self.setCentralWidget(w)
def toggle_window0(self, checked):
if self.window0.isVisible():
self.window0.hide()
else:
self.window0.show()
def toggle_window1(self):
if self.window1.isVisible():
self.window1.hide()
else:
self.window1.show()
def toggle_window2(self):
if self.window2.isVisible():
self.window2.hide()
else:
self.window2.show()
def toggle_window3(self, checked):
if self.window3.isVisible():
self.window3.hide()
else:
self.window3.show()
if __name__=="__main__":
app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
w.show()
app.exec()
To test it further, I extended the list to a list of random lengths (more than 10), where I reassured that the issue persist for specific indexes each time. For example if I create 20 buttons using the first approach, the same bug appears for - the 4rth, the 12fth and the last index exclusively - but not for the rest of them. I even tested it on a different machine. Having also searched in forums, I could not find a solution.
Do I do anything completely wrong here? Does anyone understands better to indicate why is this happening?
I kindly thank you in advance!
Environment: Ubuntu 22.04
Pyqt version : 1.9 (under conda)

Your problem is the following:
self.buttons[i].clicked.connect(self.toggle_window,i)
You are passing i as second argument to connect and expect the toggle_window function to be called with this argument. This is not happening. In toggle_window, i will always be False. See musicamente's comment regarding what this second argument to connect does.
What you should do instead is connect the button click to a function of your window object. From there, you can of course do a callback to a function of your main window as illustrated below:
import sys
from random import randint
from PyQt5 import QtWidgets
class AnotherWindow(QtWidgets.QWidget):
def __init__(self, parent, i):
super().__init__()
self.parent = parent
self.i = i
layout = QtWidgets.QVBoxLayout()
self.label = QtWidgets.QLabel("Another Window {}".format(i))
layout.addWidget(self.label)
self.setLayout(layout)
def toggle(self):
print("Toggling windows {}".format(self.i))
if self.isVisible():
self.hide()
self.parent.window_toggled(self.i, False)
else:
self.show()
self.parent.window_toggled(self.i, True)
class MainWindow(QtWidgets.QMainWindow):
def __init__(self, windows):
super().__init__()
self.windows=[]
self.buttons=[]
l=QtWidgets.QVBoxLayout()
for i,title in enumerate(windows):
window=AnotherWindow(self, i)
self.windows.append(window)
button=QtWidgets.QPushButton(title)
button.clicked.connect(window.toggle)
l.addWidget(button)
self.buttons.append(button)
w = QtWidgets.QWidget()
w.setLayout(l)
self.setCentralWidget(w)
def window_toggled(self, i, visible):
print("Window {} is now {}".format(i, "visible" if visible else "hidden"))
if __name__=="__main__":
app = QtWidgets.QApplication(sys.argv)
windows = ["window {}".format(i) for i in range(12)]
w = MainWindow(windows)
w.show()
app.exec()

How to customize Qtreewidget item editor in PyQt5?

I am making a QtreeWidget with item editable,but the problem is with the Item Editor or QAbstractItemDelegate(might be called like this,not sure).I am unable to change the stylesheet,actually i dont know how to do this.And also i want the selected lines(blue in editor) should be according to my wish.like below picture
here i want that blue selected line upto ".jpg",so that anyone cant change that ".jpg". Only ,one can change upto this".jpg"
Here is my code:
import sys
from PyQt5 import QtCore, QtWidgets
class Window(QtWidgets.QWidget):
def __init__(self):
super().__init__()
self.button = QtWidgets.QPushButton('Edit')
self.button.clicked.connect(self.edittreeitem)
self.tree = QtWidgets.QTreeWidget()
self.tree.setStyleSheet('background:#333333;color:grey')
layout = QtWidgets.QVBoxLayout(self)
layout.addWidget(self.tree)
layout.addWidget(self.button)
columns = 'ABCDE'
self.tree.setColumnCount(len(columns))
for index in range(50):
item=QtWidgets.QTreeWidgetItem(
self.tree, [f'{char}{index:02}.jpg' for char in columns])
item.setFlags(item.flags()|QtCore.Qt.ItemIsEditable)
def edittreeitem(self):
getSelected = self.tree.selectedItems()
self.tree.editItem(getSelected[0],0)
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
window = Window()
window.setWindowTitle('Test')
window.setGeometry(800, 100, 540, 300)
window.show()
sys.exit(app.exec_())

You can create your own delegate that only considers the base name without the extension, and then set the data using the existing extension.
class BaseNameDelegate(QtWidgets.QStyledItemDelegate):
def setEditorData(self, editor, index):
editor.setText(QtCore.QFileInfo(index.data()).completeBaseName())
def setModelData(self, editor, model, index):
name = editor.text()
if not name:
return
suffix = QtCore.QFileInfo(index.data()).suffix()
model.setData(index, '{}.{}'.format(name, suffix))
class Window(QtWidgets.QWidget):
def __init__(self):
# ...
self.tree.setItemDelegate(BaseNameDelegate(self.tree))
The only drawback of this is that the extension is not visible during editing, but that would require an implementation that is a bit more complex than that, as QLineEdit (the default editor for string values of a delegate) doesn't provide such behavior.

The layout is incorrect after remove widget

I am implement my project using pyqt5. Currently, I have a window including many widget. Now, I want to remove some widgets. The window looks like:
Now, I want to remove the 'name1' widget including the QLabel and QPushButton.
However, after removing all 'name1' widgets, the 'name2' widgets including QLabel and QPushButton can not self-adapte with the window, like:
All my code is:
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys
class Window(QDialog):
def __init__(self):
super().__init__()
self.initGUI()
self.show()
def initGUI(self):
layout = QVBoxLayout()
self.setLayout(layout)
removeLayout = QHBoxLayout()
self.__removeText = QLineEdit()
self.__removeBtn = QPushButton('Remove')
self.__removeBtn.clicked.connect(self.remove)
removeLayout.addWidget(self.__removeText)
removeLayout.addWidget(self.__removeBtn)
ROIsLayout = QVBoxLayout()
for name in ['name1', 'name2']:
subLayout = QHBoxLayout()
subText = QLabel(name)
subText.setObjectName(name)
subBtn = QPushButton(name)
subBtn.setObjectName(name)
subLayout.addWidget(subText)
subLayout.addWidget(subBtn)
ROIsLayout.addLayout(subLayout)
layout.addLayout(removeLayout)
layout.addLayout(ROIsLayout)
self.__ROIsLayout = ROIsLayout
def remove(self, checked=False):
name = self.__removeText.text()
while True:
child = self.__ROIsLayout.takeAt(0)
if child == None:
break
while True:
subChild = child.takeAt(0)
if subChild == None:
break
obName = subChild.widget().objectName()
if name == obName:
widget = subChild.widget()
widget.setParent(None)
child.removeWidget(widget)
self.__ROIsLayout.removeWidget(widget)
del widget
if __name__ == '__main__':
app = QApplication(sys.argv)
window = Window()
sys.exit(app.exec_())
update:
Actually, the issue may be the takeAt. The following code is workable:
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
import sys
class Window(QDialog):
def __init__(self):
super().__init__()
self.initGUI()
self.show()
def initGUI(self):
layout = QVBoxLayout()
self.setLayout(layout)
removeLayout = QHBoxLayout()
self.__removeText = QLineEdit()
self.__removeBtn = QPushButton('Remove')
self.__removeBtn.clicked.connect(self.remove)
removeLayout.addWidget(self.__removeText)
removeLayout.addWidget(self.__removeBtn)
ROIsLayout = QVBoxLayout()
for name in ['name1', 'name2']:
subLayout = QHBoxLayout()
subLayout.setObjectName(name)
subText = QLabel(name, parent=self)
subText.setObjectName(name)
subBtn = QPushButton(name, parent=self)
subBtn.setObjectName(name)
subLayout.addWidget(subText)
subLayout.addWidget(subBtn)
ROIsLayout.addLayout(subLayout)
print(name, subLayout, subText, subBtn)
layout.addLayout(removeLayout)
layout.addLayout(ROIsLayout)
self.__ROIsLayout = ROIsLayout
self.record = [subLayout, subText, subBtn]
def remove(self, checked=False):
layout = self.record[0]
txt = self.record[1]
btn = self.record[2]
layout.removeWidget(txt)
txt.setParent(None)
txt.deleteLater()
layout.removeWidget(btn)
btn.setParent(None)
btn.deleteLater()
if __name__ == '__main__':
app = QApplication(sys.argv)
window = Window()
sys.exit(app.exec_())
But, I have printed the QLabel/QPushButton in the self.record, and I find it is the same with that from child.takeAt(0).widget().

The main issue in your code is that you're constantly using takeAt(). The result is that all items in the __ROIsLayout layout will be removed from it (but not deleted), which, in your case, are the sub layouts. This is clearly not a good approach: only the widgets with the corresponding object name will be actually deleted, while the others will still be "owned" by their previous parent, will still be visible at their previous position and their geometries won't be updated since they're not managed by the layout anymore.
There are multiple solutions to your question, all depending on your needs.
If you need to remove rows from a layout, I'd consider setting the object name on the layout instead, and look for it using self.findChild().
Also consider that, while Qt allows setting the same object name for more than one object, that's not suggested.
Finally, while using del is normally enough, it's usually better to call deleteLater() for all Qt objects, which ensures that Qt correctly removes all objects (and related parentship/connections).
Another possibility, for this specific case, is to use a QFormLayout.

How to change color of whitespace characters?

I'm making a text editor using Qt and Python(PySide2). Like most other text editors, I want to make visible whitespaces(space, tab, new line...) and succeed it. QTextEdit and QTextOption show whitespace characters as visible special characters. (space to dot, tab to arrow, new line to reverse-P)
But the colors of those special characters are same with other characters. I think it will be more readable if the colors are different.
How to change the color of the special characters of whitespaces?
orgText = """
\t\tAll those moments
\t\twill be lost
in time
like tears
in rain.
It's time to die."""
option = QtGui.QTextOption()
option.setFlags(QtGui.QTextOption.ShowTabsAndSpaces | QtGui.QTextOption.ShowLineAndParagraphSeparators)
self.teOrg.setPlainText(orgText)
self.teOrg.document().setDefaultTextOption(option)

If you want to give a special based on the text then you should use QSyntaxHighlighter. To do this you must get the start and end of the pattern and change the format using setFormat().
I could only modify the format of the space (" ") and the tab ("\t") but not the paragraph separators(¶):
import re
from PySide2 import QtCore, QtGui, QtWidgets
orgText = """
\t\tAll those moments
\t\twill be lost
in time
like tears
in rain.
It's time to die."""
class Highlighter(QtGui.QSyntaxHighlighter):
def __init__(self, parent=None):
super(Highlighter, self).__init__(parent)
space_format = QtGui.QTextCharFormat()
space_format.setBackground(QtGui.QColor("salmon"))
tab_format = QtGui.QTextCharFormat()
tab_format.setBackground(QtGui.QColor("lightgray"))
self.highlightingRules = [
(r"( )\1*", space_format),
(r"(\t)\1*", tab_format),
]
def highlightBlock(self, text):
for pattern, fmt in self.highlightingRules:
expression = re.compile(pattern)
m = expression.search(text)
while m is not None:
start, end = m.span()
self.setFormat(start, end - start, fmt)
m = expression.search(text, end + 1)
class MainWindow(QtWidgets.QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.teOrg = QtWidgets.QTextEdit()
self.setCentralWidget(self.teOrg)
self.teOrg.setPlainText(orgText)
option = QtGui.QTextOption()
option.setFlags(
QtGui.QTextOption.ShowTabsAndSpaces
| QtGui.QTextOption.ShowLineAndParagraphSeparators
)
self.teOrg.document().setDefaultTextOption(option)
self.highlighter = Highlighter(self.teOrg.document())
if __name__ == "__main__":
import sys
app = QtWidgets.QApplication(sys.argv)
w = MainWindow()
w.resize(320, 240)
w.show()
sys.exit(app.exec_())

Finally, I rewrote #eyllanesc's code.
import sys
import typing
import re
from PySide2 import QtCore
from PySide2 import QtGui
from PySide2 import QtWidgets
class SyntaxHighlighter(QtGui.QSyntaxHighlighter):
def __init__(self, parent:typing.Union[QtCore.QObject, QtGui.QTextDocument, None]=None):
super().__init__(parent)
self.spaceFmt = QtGui.QTextCharFormat()
self.spaceFmt.setForeground(QtGui.QColor('red'))
self.expression = re.compile(r'\s+', re.U | re.S | re.M)
def highlightBlock(self, text:str):
for match in self.expression.finditer(text):
start, end = match.span()
self.setFormat(start, end - start, self.spaceFmt)
class TextEditWin(QtWidgets.QMainWindow):
def __init__(self):
# Initialize ui.
super().__init__()
self.resize(800, 600)
self.textEdit = QtWidgets.QTextEdit(self)
self.setCentralWidget(self.textEdit)
self.textEdit.setFontPointSize(15)
# Make space characters visible.
option = QtGui.QTextOption()
option.setFlags(QtGui.QTextOption.ShowTabsAndSpaces | QtGui.QTextOption.ShowLineAndParagraphSeparators)
self.textEdit.document().setDefaultTextOption(option)
# Change color of space characters.
self.highlighter = SyntaxHighlighter(self.textEdit.document())
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
win = TextEditWin()
win.show()
sys.exit(app.exec_())
My code do not change color of the paragraph separators(¶) either. I think it is because Qt delivers the text except '\n' when highlightBlock() called.
Thanks #eyllanesc.

How to change languages(translations) dynamically on PyQt5?

I wonder if it is possible to change the languages(translations) dynamically without using qt designer to make the UI? That means I don't want to use the function retranslateUi() to update the program interface.
Here is my code, but I'm stuck on lines marked #1 #2 #3. Don't know what I should use to update the interface.
import sys
from PyQt5.QtCore import Qt, QTranslator
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QLabel,
QComboBox, QVBoxLayout
class Demo(QWidget):
def __init__(self):
super(Demo, self).__init__()
self.button = QPushButton(self.tr('Start'), self)
self.label = QLabel(self.tr('Hello, World'), self)
self.label.setAlignment(Qt.AlignCenter)
self.combo = QComboBox(self)
self.combo.addItem('English')
self.combo.addItem('中文')
self.combo.addItem('français')
self.combo.currentTextChanged.connect(self.change_func)
self.trans = QTranslator(self)
self.v_layout = QVBoxLayout()
self.v_layout.addWidget(self.combo)
self.v_layout.addWidget(self.button)
self.v_layout.addWidget(self.label)
self.setLayout(self.v_layout)
def change_func(self):
print(self.combo.currentText())
if self.combo.currentText() == '中文':
self.trans.load('eng-chs')
_app = QApplication.instance()
_app.installTranslator(self.trans)
# 1
elif self.combo.currentText() == 'français':
self.trans.load('eng-fr')
_app = QApplication.instance()
_app.installTranslator(self.trans)
# 2
else:
_app = QApplication.instance()
_app.removeTranslator(self.trans)
# 3
if __name__ == '__main__':
app = QApplication(sys.argv)
demo = Demo()
demo.show()
sys.exit(app.exec_())
Any help would be appreciated.

TL; DR; It is not necessary to use Qt Designer
You should not use Qt Designer necessarily but you should use the same technique, that is, create a method that could be called retranslateUi() and in it set the texts using translate() instead of tr() (for more details read the docs). Calling that method when you change language for it must use the changeEvent() event. For example in your case the code is as follows:
import sys
from PyQt5 import QtCore, QtGui, QtWidgets
class Demo(QtWidgets.QWidget):
def __init__(self):
super(Demo, self).__init__()
self.button = QtWidgets.QPushButton()
self.label = QtWidgets.QLabel(alignment=QtCore.Qt.AlignCenter)
self.combo = QtWidgets.QComboBox(self)
self.combo.currentIndexChanged.connect(self.change_func)
self.trans = QtCore.QTranslator(self)
self.v_layout = QtWidgets.QVBoxLayout(self)
self.v_layout.addWidget(self.combo)
self.v_layout.addWidget(self.button)
self.v_layout.addWidget(self.label)
options = ([('English', ''), ('français', 'eng-fr' ), ('中文', 'eng-chs'), ])
for i, (text, lang) in enumerate(options):
self.combo.addItem(text)
self.combo.setItemData(i, lang)
self.retranslateUi()
#QtCore.pyqtSlot(int)
def change_func(self, index):
data = self.combo.itemData(index)
if data:
self.trans.load(data)
QtWidgets.QApplication.instance().installTranslator(self.trans)
else:
QtWidgets.QApplication.instance().removeTranslator(self.trans)
def changeEvent(self, event):
if event.type() == QtCore.QEvent.LanguageChange:
self.retranslateUi()
super(Demo, self).changeEvent(event)
def retranslateUi(self):
self.button.setText(QtWidgets.QApplication.translate('Demo', 'Start'))
self.label.setText(QtWidgets.QApplication.translate('Demo', 'Hello, World'))
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
demo = Demo()
demo.show()
sys.exit(app.exec_())
Then generate the .ts:
pylupdate5 main.py -ts eng-chs.ts
pylupdate5 main.py -ts eng-fr.ts
Then use Qt Linguist to do the translations.
And finally the .qm:
lrelease eng-fr.ts eng-chs.qm
The complete project you find here.

No you will have to use a technique like Qt Designer does with retranslateUi because the Qt widget system does not have a way to redo the translation on it's own (otherwise QT Designer would be using that to).
Building such a system would require a fundamental change to the widgets as for each string property you would need to know that it contains a translatable string (not a data value) and knowing the original string for looking up the new translation would be best (reversing translations could be ambiguous).