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Updated: How to reduce QWidget nesting in PyQt code?

Updated Question
I think my original quandary might be a result of the structure of my PyQt app. The way I've approached creating a GUI is to divide the larger widget into smaller pieces, each given their own class until the parts are simple enough. Because of this, I end up with a ton of nesting, as a large widget holds instances of smaller widgets, and those hold their own even smaller widgets. It makes it hard to navigate data around the app.
How should a PyQt app be structured so that it is simple to understand in code and yet has a structure containing very little nesting? I haven't found many examples of this around, so I'm sort of stuck. The code example in my original question shows a pretty good example of the structure I'm currently using, which has a large amount of nesting.
Info on program
The GUI is used to create a set of parameters for running a test. The options in each setting should correspond to a binary number, and all of the binary numbers indicated by each set of options are collected, formed into a single sequence of binary numbers, and passed on. Changes to settings do not have to be carried over between sessions, as each new session will most likely correspond to a new test (and thus a new set of choices for settings).
The basic flow of the app should be that upon opening it, all available settings (about 20 total) are set to their default values. A user can go through and change whatever settings they would like, and once they're done they can press a "Generate" button to gather all of the binary numbers corresponding to the settings and create the command. It would be very helpful to have a live preview of individual bits that updates as settings are changed, which is why updates must be immediate.
Some settings are dependent on other; for instance, Setting A has 4 options, and if option 3 is selected, Setting B should be made visible, otherwise it is invisible.
Original Question
I'm definitely a beginner to PyQt, so I don't quite know if I've worded my question correctly, but here goes. I've got a GUI wherein I'm attempting to take a bunch of different settings, keep track of what number was selected from each setting, and then pass the number up to an object that keeps track of all of the numbers from all of the settings. The trouble is that I don't know the best way to get all the individual settings values up my tree of classes, so to speak. Here's the structure of my GUI so far:
Bottom: individual custom QWidgets, each responsible for a single setting. Each has a signal that fires whenever the value it returns changes.
Middle: a QWidget containing ~7-10 individual settings each. These collect settings into related groups.
Top: a QTabWidget that places each instance of a setting group into an individual tab. This widget also contains an object that should ideally collect all of the settings from individual groups into it.
My question is how do I get the values from the bottom layer signals to the top layer widget? My only idea is to connect all of the signals from those small setting widgets to a signal in the middle layer, and connect the middle layer signal to something in the top layer. This sort of chaining seems crazy, though.
I'm running PyQt5 and Python 3.7.
Here's some stripped down code which hopefully shows what I want to do.
class TabWindow(QTabWidget):
def __init__(self):
super().__init__()
self.tabs = [SettingsGroup1, SettingsGroup2, SettingsGroup3]
self.setting_storage = { # dictionary is where I'd like to store all settings values
# 'setting name': setting value
}
for tab in self.tabs:
self.addTab(tab, 'Example')
class SettingsGroup(QWidget):
def __init__(self):
super().__init__()
# not shown: layout created for widget
self.settings = []
def add_to_group(self, new_setting):
self.settings.append(new_setting)
# not shown: add setting to the layout
class SettingsGroup1(SettingsGroup):
def __init__(self):
super().__init__()
self.add_to_group([Setting1, Setting2, Setting3])
class SettingsGroup2(SettingsGroup):...
class SettingsGroup3(SettingsGroup):...
class Setting(QWidget):
val_signal = pyqtSignal([int], name='valChanged')
def __init__(self, name):
self.val = None
self.name = name
def set_val(self, new_val):
self.val = new_val
self.val_signal.emit(self.val) # <-- the signal I want to pass up
class Setting1(Setting):
def __init__(self, name):
super().__init__(name)
# not shown: create custom setting layout/interface
class Setting2(Setting):...
class Setting3(Setting):...
I use a lot of inheritance (SettingsGroup -> SettingsGroup1, 2, 3) because each subclass will have its own functions and internal dependencies that are unique to it. For each Setting subclass, for instance, there is a different user interface.
Thanks for any help provided!

EDIT: The question has been updated in the meantime, I've added a solution that's more specific at the bottom of this answer.
I feel like this question is slightly "opinion based", but since I've had my share of similar situations I'd like to propose my suggestions. In these situations it's important to understand that there's not one good way to do things, but many ways to do it wrong.
Original answer
An idea could be to create a common signal interface for every "level", which will get that signal and send it back to its parent by adding its own name to keep track of the setting "path"; the topmost widget will then evaluate the changes accordingly.
In this example every tab "group" has its own valueChanged signal, which includes the group name, setting name and value; the source signal is fired from the "source" (a spinbox, in this case), then it follows its parents which, in turn "add" their name in turn.
Keep in mind that you can also just use a generalized pyqtSignal(object) for every parent and connect it with widget.valueChanged.connect(self.valueChanged), and then track its group and setting by walking by self.sender() parents backwards.
As a final notice, if you are using these values for application settings, remember that Qt already provides the QSettings API, which can be used as a common and OS-transparent interface for every configuration you need to set (and remember between sessions) in your application. I implemented it in the example, but I suggest you to read its documentation to better understand how it works.
import sys
from PyQt5 import QtCore, QtWidgets
class SettingWidget(QtWidgets.QWidget):
valueChanged = QtCore.pyqtSignal(int)
def __init__(self, name):
super().__init__()
self.settings = QtCore.QSettings()
self.val = 0
self.name = name
layout = QtWidgets.QVBoxLayout()
self.setLayout(layout)
layout.addWidget(QtWidgets.QLabel(self.name))
self.spinBox = QtWidgets.QSpinBox()
layout.addWidget(self.spinBox)
self.spinBox.valueChanged.connect(self.set_val)
def set_val(self, new_val):
if self.val != new_val:
self.val = new_val
self.valueChanged.emit(self.val)
# enter a setting group, ensuring that same name settings won't
# be mismatched; this allows a single sub level setting only
self.settings.beginGroup(self.parent().name)
self.settings.setValue(self.name, new_val)
# leave the setting group. THIS IS IMPORTANT!!!
self.settings.endGroup()
class SettingWidget1(SettingWidget):
def __init__(self):
super().__init__('Setting1')
class SettingWidget2(SettingWidget):
def __init__(self):
super().__init__('Setting2')
class SettingWidget3(SettingWidget):
def __init__(self):
super().__init__('Setting3')
class SettingsGroup(QtWidgets.QWidget):
# create two signal signatures, the first sends the full "path",
# while the last will just send the value
valueChanged = QtCore.pyqtSignal([str, str, int], [int])
def __init__(self, name):
super().__init__()
self.name = name
layout = QtWidgets.QHBoxLayout()
self.setLayout(layout)
def add_to_group(self, new_setting):
widget = new_setting()
# emit both signal signatures
widget.valueChanged.connect(
lambda value, name=widget.name: self.valueChanged.emit(
self.name, name, value))
widget.valueChanged.connect(self.valueChanged[int])
self.layout().addWidget(widget)
class SettingsGroup1(SettingsGroup):
def __init__(self):
super().__init__('Group1')
self.add_to_group(SettingWidget1)
self.add_to_group(SettingWidget2)
class SettingsGroup2(SettingsGroup):
def __init__(self):
super().__init__('Group2')
self.add_to_group(SettingWidget3)
class TabWidget(QtWidgets.QTabWidget):
def __init__(self):
QtWidgets.QTabWidget.__init__(self)
self.settings = QtCore.QSettings()
self.tabs = [SettingsGroup1, SettingsGroup2]
self.settingsDict = {}
for tab in self.tabs:
widget = tab()
self.addTab(widget, widget.__class__.__name__)
widget.valueChanged[str, str, int].connect(self.valueChangedFullPath)
widget.valueChanged[int].connect(self.valueChangedOnly)
def valueChangedFullPath(self, group, setting, value):
# update the settings dict; if the group key doesn't exist, create it
try:
self.settingsDict[group][setting] = value
except:
self.settingsDict[group] = {setting: value}
settingsData = [group, setting, value]
print('Full path result: {}'.format(settingsData))
# Apply setting from here, instead of using the SettingWidget
# settings.setValue() option; this allows a single sub level only
# self.applySetting(data)
def valueChangedOnly(self, value):
parent = sender = self.sender()
# sender() returns the last signal sender, so we need to track down its
# source; keep in mind that this is *not* a suggested approach, as
# tracking the source might result in recursion if the sender's sender
# is not one of its children; this system also has issues if you're
# using a Qt.DirectConnection from a thread different from the one that
# emitted it
while parent.sender() in sender.children():
parent = sender.sender()
widgetPath = []
while parent not in self.children():
widgetPath.insert(0, parent)
parent = parent.parent()
settingsData = [w.name for w in widgetPath] + [value]
print('Single value result: {}'.format(settingsData))
# similar to valueChangedFullPath(), but with this implementation more
# nested "levels" can be used instead
# self.applySetting(settingsData)
def applySetting(self, settingsData):
# walk up to the next to last of settingsData levels, assuming they are
# all parent group section names
for count, group in enumerate(settingsData[:-2], 1):
self.settings.beginGroup(group)
# set the setting name settingsData[-2] to its value settingsData[-1]
self.settings.setValue(*settingsData[-2:])
for g in range(count):
self.settings.endGroup()
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
# set both Organization and Application name to make settings persistent
app.setOrganizationName('StackOverflow')
app.setApplicationName('Example')
w = TabWidget()
w.show()
sys.exit(app.exec_())
Alternate solution, based on updated answer
Since the answer has become more specific in its update, I'm adding another suggestion.
As far as we can understand now, you don't need that level of "nested" classes, but more specifically designed code that can be reused according to your purposes. Also, since you're using binary based data, it makes things a bit (pun intended) easier, as long as you know how bit operation works (which I assume you do) and the setting "widgets" don't require specific GUI customization.
In this example I created just one "setting" class and one "group" class, and their instancies are created only according to their names and default values.
import sys
from PyQt5 import QtCore, QtWidgets
defaultValues = '0010101', '1001010', '000111'
# set bit lengths for each setting; be careful in ensuring that each
# setting group has the full default value bit length!
groups = [
['Group 1', [1, 3, 2, 1]],
['Group 2', [1, 2, 2, 1, 1]],
['Group 1', [2, 1, 2, 1]],
]
class BinaryWidget(QtWidgets.QFrame):
changed = QtCore.pyqtSignal()
def __init__(self, name, index, defaults='0'):
QtWidgets.QFrame.__init__(self)
self.setFrameShape(self.StyledPanel|self.Sunken)
layout = QtWidgets.QGridLayout()
self.setLayout(layout)
self.index = index
self.defaults = defaults
self.buttons = []
# use the "defaults" length to create buttons
for i in range(len(defaults)):
value = int(defaults[i], 2) & 1
# I used QToolButtons as they're usually smaller than QPushButtons
btn = QtWidgets.QToolButton()
btn.setText(str(value))
layout.addWidget(btn, 1, i)
btn.setCheckable(True)
btn.setChecked(value)
btn.toggled.connect(self.changed)
# show the binary value on change, just for conveniency
btn.toggled.connect(lambda v, btn=btn: btn.setText(str(int(v))))
self.buttons.append(btn)
layout.addWidget(QtWidgets.QLabel(name), 0, 0, 1, layout.columnCount())
def value(self):
# return the correct value of all widget's buttons; they're reversed
# because of how bit shifting works
v = 0
for i, btn in enumerate(reversed(self.buttons)):
v += btn.isChecked() << i
# bit shift again, according to the actual "setting" bit index
return v << self.index
def resetValues(self):
oldValue = self.value()
self.blockSignals(True)
for i, value in enumerate(self.defaults):
self.buttons[i].setChecked(int(self.defaults[i], 2) & 1)
self.blockSignals(False)
newValue = self.value()
# emit the changed signal only once, and only if values actually changed
if oldValue != newValue:
self.changed.emit()
class Group(QtWidgets.QWidget):
changed = QtCore.pyqtSignal()
def __init__(self, name, defaults=None, lenghts=None):
QtWidgets.QWidget.__init__(self)
layout = QtWidgets.QHBoxLayout()
self.setLayout(layout)
self.name = name
self.bitLength = 0
self.widgets = []
if defaults is not None:
self.addOptions(defaults, lenghts)
def value(self):
v = 0
for widget in self.widgets:
v += widget.value()
return v
def addOption(self, name, index, default='0'):
widget = BinaryWidget(name, index, default)
self.layout().addWidget(widget)
self.widgets.append(widget)
widget.changed.connect(self.changed)
self.bitLength += len(default)
def addOptions(self, defaults, lenghts = None):
if lenghts is None:
lenghts = [1] * len(defaults)
# reverse bit order for per-setting indexing
defaultsIndex = 0
bitIndex = len(defaults)
for i, l in enumerate(lenghts):
self.addOption(
'Setting {}'.format(i + 1),
bitIndex - l,
defaults[defaultsIndex:defaultsIndex + l])
bitIndex -= l
defaultsIndex += l
def resetValues(self):
for widget in self.widgets:
widget.resetValues()
class Tester(QtWidgets.QWidget):
def __init__(self):
QtWidgets.QWidget.__init__(self)
layout = QtWidgets.QGridLayout()
self.setLayout(layout)
self.tabWidget = QtWidgets.QTabWidget()
layout.addWidget(self.tabWidget)
resultLayout = QtWidgets.QHBoxLayout()
layout.addLayout(resultLayout, layout.rowCount(), 0, 1, layout.columnCount())
self.tabs = []
self.labels = []
for (group, lenghts), defaults in zip(groups, defaultValues):
tab = Group(group, defaults, lenghts)
self.tabWidget.addTab(tab, group)
tab.changed.connect(self.updateResults)
self.tabs.append(tab)
tabLabel = QtWidgets.QLabel()
self.labels.append(tabLabel)
resultLayout.addWidget(tabLabel)
self.resetButton = QtWidgets.QPushButton('Reset values')
layout.addWidget(self.resetButton)
self.resetButton.clicked.connect(lambda: [tab.resetValues() for tab in self.tabs])
self.updateResults()
def values(self):
return [tab.value() for tab in self.tabs]
def updateResults(self):
for value, tab, label in zip(self.values(), self.tabs, self.labels):
label.setText('''
{0}: <span style="font-family:monospace;">{1} <b>{1:0{2}b}</b></span>
'''.format(tab.name, value, tab.bitLength))
if __name__ == '__main__':
app = QtWidgets.QApplication(sys.argv)
w = Tester()
w.show()
sys.exit(app.exec_())

QGraphicsScene changing objects when selected

I have a QGraphicsScene containing some simple objects (in this simplified example circles) that I want to change into other objects (here squares) when selected. More specifically I'd like to have parent objects which don't draw themselves, they are drawn by their child objects, and under various circumstances, but in particular when the parent objects are selected, I'd like the set of child objects to change. This is a nice conceptual framework for the overall app I am working on.
So I've implemented this in PySide and I thought it was working fine: the circles change nicely into squares when you click on them.
Until I use RubberBandDrag selection in the view. This causes an instant segfault when the rubber band selection reaches the parent object and the selection changes. Presumably this is being triggered because the rubber band selection in QT is somehow keeping a pointer to the child item which is disappearing before the rubber band selection action is complete.
Simplified code below - test it by first clicking on the object (it changes nicely) then dragging over the object - segfault:
from PySide import QtCore,QtGui
class SceneObject(QtGui.QGraphicsItem):
def __init__(self, scene):
QtGui.QGraphicsItem.__init__(self, scene = scene)
self.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, True)
self.setFlag(QtGui.QGraphicsItem.ItemHasNoContents, True)
self.updateContents()
def updateContents(self):
self.prepareGeometryChange()
for c in self.childItems():
self.scene().removeItem(c)
if self.isSelected():
shape_item = QtGui.QGraphicsRectItem()
else:
shape_item = QtGui.QGraphicsEllipseItem()
shape_item.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, False)
shape_item.setFlag(QtGui.QGraphicsItem.ItemStacksBehindParent,True)
shape_item.setPen(QtGui.QPen("green"))
shape_item.setRect(QtCore.QRectF(0,0,10,10))
shape_item.setParentItem(self)
def itemChange(self, change, value):
if self.scene() != None:
if change == QtGui.QGraphicsItem.ItemSelectedHasChanged:
self.updateContents()
return
return super(SceneObject,self).itemChange(change, value)
def boundingRect(self):
return self.childrenBoundingRect()
class Visualiser(QtGui.QMainWindow):
def __init__(self):
super(Visualiser,self).__init__()
self.viewer = QtGui.QGraphicsView(self)
self.viewer.setDragMode(QtGui.QGraphicsView.RubberBandDrag)
self.setCentralWidget(self.viewer)
self.viewer.setScene(QtGui.QGraphicsScene())
parent_item = SceneObject(self.viewer.scene())
parent_item.setPos(50,50)
app = QtGui.QApplication([])
mainwindow = Visualiser()
mainwindow.show()
app.exec_()
So questions:
Have I just made a mistake that can be straightforwardly fixed?
Or is removing objects from the scene not allowed when handling an ItemSelectedHasChanged event?
Is there a handy workaround? Or what's a good alternative approach? I could replace the QGraphicsRectItem with a custom item which can be drawn either as a square or a circle but that doesn't conveniently cover all my use cases. I can see that I could make that work but it will certainly not be as straightforward.
EDIT - Workaround:
It is possible to prevent this failing by preserving the about-to-be-deleted object for a while. This can be done by something like this:
def updateContents(self):
self.prepareGeometryChange()
self._temp_store = self.childItems()
for c in self.childItems():
self.scene().removeItem(c)
...
However, this is ugly code and increases the memory usage for no real benefit. Instead I have moved to using the QGraphicsScene.selectionChanged signal as suggested in this answer.

I've debugged it. Reproduced on Lunix
1 qFatal(const char *, ...) *plt 0x7f05d4e81c40
2 qt_assert qglobal.cpp 2054 0x7f05d4ea197e
3 QScopedPointer<QGraphicsItemPrivate, QScopedPointerDeleter<QGraphicsItemPrivate>>::operator-> qscopedpointer.h 112 0x7f05d2c767ec
4 QGraphicsItem::flags qgraphicsitem.cpp 1799 0x7f05d2c573b8
5 QGraphicsScene::setSelectionArea qgraphicsscene.cpp 2381 0x7f05d2c94893
6 QGraphicsView::mouseMoveEvent qgraphicsview.cpp 3257 0x7f05d2cca553
7 QGraphicsViewWrapper::mouseMoveEvent qgraphicsview_wrapper.cpp 1023 0x7f05d362be83
8 QWidget::event qwidget.cpp 8374 0x7f05d2570371
qt-everywhere-opensource-src-4.8.6/src/gui/graphicsview/qgraphicsscene.cpp:2381
void QGraphicsScene::setSelectionArea(const QPainterPath &path, Qt::ItemSelectionMode mode,
const QTransform &deviceTransform)
{
...
// Set all items in path to selected.
foreach (QGraphicsItem *item, items(path, mode, Qt::DescendingOrder, deviceTransform)) {
if (item->flags() & QGraphicsItem::ItemIsSelectable) { // item is invalid here
if (!item->isSelected())
changed = true;
unselectItems.remove(item);
item->setSelected(true);
}
}
They are using items() function to find a list of items under the rubber band selection. But if one item while processing deletes something the item pointer just becomes invalid. And next call to item->flags() causes the crash.
As alternative you could use QGraphicsScene::selectionChanged signal. It's emitted only once per selection change.
Looks like it's not expected by Qt to have some major changes in itemChange
Behind of this here is common mistake you have with prepareGeometryChange() call.
It's designed to be called right before changing boundingRect. Bounding rect should be the old one when prepareGeometryChange called and new one right after.
So that's could happen:
In updateContents:
self.prepareGeometryChange(); # calls boundingRect. old value returned
...
shape_item.setParentItem(self); # could call the boundingRect. but still old value returned!
After child added it calls boundingRect again but value unexpected different.
As a solution you can add a variable
def updateContents(self):
for c in self.childItems():
self.scene().removeItem(c)
if self.isSelected():
shape_item = QtGui.QGraphicsRectItem()
else:
shape_item = QtGui.QGraphicsEllipseItem()
shape_item.setFlag(QtGui.QGraphicsItem.ItemIsSelectable, False)
shape_item.setFlag(QtGui.QGraphicsItem.ItemStacksBehindParent,True)
shape_item.setPen(QtGui.QPen("green"))
shape_item.setRect(QtCore.QRectF(0,0,10,10))
shape_item.setParentItem(self)
self.prepareGeometryChange();
self._childRect = self.childrenBoundingRect()
def boundingRect(self):
return self._childRect

How to undo an edit of a QListWidgetItem in PySide/PyQt?

Short version
How do you implement undo functionality for edits made on QListWidgetItems in PySide/PyQt?
Hint from a Qt tutorial?
The following tutorial written for Qt users (c++) likely has the answer, but I am not a c++ person, so get a bit lost: Using Undo/Redo with Item Views
Longer version
I am using a QListWidget to learn my way around PyQt's Undo Framework (with the help of an article on the topic). I am fine with undo/redo when I implement a command myself (like deleting an item from the list).
I also want to make the QListWidgetItems in the widget editable. This is easy enough: just add the ItemIsEditable flag to each item. The problem is, how can I push such edits onto the undo stack, so I can then undo/redo them?
Below is a simple working example that shows a list, lets you delete items,and undo/redo such deletions. The application displays both the list and the the undo stack. What needs to be done to get edits onto that stack?
Simple working example
from PySide import QtGui, QtCore
class TodoList(QtGui.QWidget):
def __init__(self):
QtGui.QWidget.__init__(self)
self.setAttribute(QtCore.Qt.WA_DeleteOnClose)
self.initUI()
self.show()
def initUI(self):
self.todoList = self.makeTodoList()
self.undoStack = QtGui.QUndoStack(self)
undoView = QtGui.QUndoView(self.undoStack)
buttonLayout = self.buttonSetup()
mainLayout = QtGui.QHBoxLayout(self)
mainLayout.addWidget(undoView)
mainLayout.addWidget(self.todoList)
mainLayout.addLayout(buttonLayout)
self.setLayout(mainLayout)
self.makeConnections()
def buttonSetup(self):
#Make buttons
self.deleteButton = QtGui.QPushButton("Delete")
self.undoButton = QtGui.QPushButton("Undo")
self.redoButton = QtGui.QPushButton("Redo")
self.quitButton = QtGui.QPushButton("Quit")
#Lay them out
buttonLayout = QtGui.QVBoxLayout()
buttonLayout.addWidget(self.deleteButton)
buttonLayout.addStretch()
buttonLayout.addWidget(self.undoButton)
buttonLayout.addWidget(self.redoButton)
buttonLayout.addStretch()
buttonLayout.addWidget(self.quitButton)
return buttonLayout
def makeConnections(self):
self.deleteButton.clicked.connect(self.deleteItem)
self.quitButton.clicked.connect(self.close)
self.undoButton.clicked.connect(self.undoStack.undo)
self.redoButton.clicked.connect(self.undoStack.redo)
def deleteItem(self):
rowSelected=self.todoList.currentRow()
rowItem = self.todoList.item(rowSelected)
if rowItem is None:
return
command = CommandDelete(self.todoList, rowItem, rowSelected,
"Delete item '{0}'".format(rowItem.text()))
self.undoStack.push(command)
def makeTodoList(self):
todoList = QtGui.QListWidget()
allTasks = ('Fix door', 'Make dinner', 'Read',
'Program in PySide', 'Be nice to everyone')
for task in allTasks:
todoItem=QtGui.QListWidgetItem(task)
todoList.addItem(todoItem)
todoItem.setFlags(QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEnabled)
return todoList
class CommandDelete(QtGui.QUndoCommand):
def __init__(self, listWidget, item, row, description):
super(CommandDelete, self).__init__(description)
self.listWidget = listWidget
self.string = item.text()
self.row = row
def redo(self):
self.listWidget.takeItem(self.row)
def undo(self):
addItem = QtGui.QListWidgetItem(self.string)
addItem.setFlags(QtCore.Qt.ItemIsSelectable | QtCore.Qt.ItemIsEnabled)
self.listWidget.insertItem(self.row, addItem)
if __name__ == "__main__":
import sys
app = QtGui.QApplication(sys.argv)
myList=TodoList()
sys.exit(app.exec_())
Note I posted an earlier version of this question at QtCentre.

That tutorial you mentioned is really not very helpful. There are indeed many approaches to undo-redo implementation for views, we just need to choose the simplest one. If you deal with small lists, the simpliest way is to save all data on each change and restore full list from scratch on each undo or redo operation.
If you still want atomic changes list, you can track user-made edits with QListWidget::itemChanged signal. There are two problems with that:
Any other item change in the list will also trigger this signal, so you need to wrap any code that changes items into QObject::blockSignals calls to block unwanted signals.
There is no way to get previous text, you can only get new text. The solution is either save all list data to variable, use and update it on change or save the edited item's text before it's edited. QListWidget is pretty reticent about its internal editor state, so I decided to use QListWidget::currentItemChanged assuming that user won't find a way to edit an item without making is current first.
So this is the changes that will make it work (besides adding ItemIsEditable flag in two places):
def __init__(self):
#...
self.todoList.itemChanged.connect(self.itemChanged)
self.todoList.currentItemChanged.connect(self.currentItemChanged)
self.textBeforeEdit = ""
def itemChanged(self, item):
command = CommandEdit(self.todoList, item, self.todoList.row(item),
self.textBeforeEdit,
"Rename item '{0}' to '{1}'".format(self.textBeforeEdit, item.text()))
self.undoStack.push(command)
def currentItemChanged(self, item):
self.textBeforeEdit = item.text()
And the new change class:
class CommandEdit(QtGui.QUndoCommand):
def __init__(self, listWidget, item, row, textBeforeEdit, description):
super(CommandEdit, self).__init__(description)
self.listWidget = listWidget
self.textBeforeEdit = textBeforeEdit
self.textAfterEdit = item.text()
self.row = row
def redo(self):
self.listWidget.blockSignals(True)
self.listWidget.item(self.row).setText(self.textAfterEdit)
self.listWidget.blockSignals(False)
def undo(self):
self.listWidget.blockSignals(True)
self.listWidget.item(self.row).setText(self.textBeforeEdit)
self.listWidget.blockSignals(False)

I would do it like this:
Create a custom QItemDelegate and use these two signals:
editorEvent
closeEditor
On editorEvent: Save current state
On closeEditor: Get new state and create a QUndoCommand that set the new state for Redo and the old state for Undo.

Each time you verify and accept the new text of the item, save it as list item data. Quasi-semi-pseudo-code:
OnItemEdited(Item* item)
{
int dataRole{ 32 }; //or greater (see ItemDataRole documentation)
if (Validate(item->text()) {
item->setData(dataRole, item->text());
} else { //Restore previous value
item->setText(item->data(dataRole).toString());
}
}
I'm sorry if it looks too much like C++.

Problems with a bind function from tkinter in Python

I am working on an application that is supposed to support both running from a console and from a GUI. The application has several options to choose from, and since in both running modes the program is going to have the same options obviously, I made a generalisation:
class Option:
def __init__(self, par_name, par_desc):
self.name = par_name
self.desc = par_desc
class Mode():
def __init__(self):
self.options = []
self.options.append(Option('Option1', 'Desc1'))
self.options.append(Option('Option2', 'Desc2'))
self.options.append(Option('Option3', 'Desc3'))
self.options.append(Option('Option4', 'Desc4'))
self.options.append(Option('Option5', 'Desc5'))
#And so on
The problem is that in GUI, those options are going to be buttons, so I have to add a new field to an Option class and I'm doing it like this:
def onMouseEnter(par_event, par_option):
helpLabel.configure(text = par_option.desc)
return
def onMouseLeave(par_event):
helpLabel.configure(text = '')
return
class GUIMode(Mode):
#...
for iOption in self.options:
iOption.button = Button(wrapper, text = iOption.name, bg = '#004A7F', fg = 'white')
iOption.button.bind('<Enter>', lambda par_event: onMouseEnter(par_event, iOption))
iOption.button.bind('<Leave>', lambda par_event: onMouseLeave(par_event))
#...
There is also a "help label" showing the description of the option every time a mouse hovers over it, so there I am binding those functions.
What is happening is that while I am indeed successfully adding a new field with a button, the bind function seems to mess up and the result is this:
Help label is always showing the description of the last option added, no matter over which button I hover. The problem seems to go away if I directly modify the Option class instead, like this:
class Option:
def __init__(self, par_name, par_desc):
self.name = par_name
self.desc = par_desc
self.button = Button(wrapper, text = self.name, bg = '#004A7F', fg = 'white')
self.button.bind('<Enter>', lambda par_event: onMouseEnter(par_event, self))
self.button.bind('<Leave>', lambda par_event: onMouseLeave(par_event))
But I obviously can't keep it that way because the console mode will get those fields too which I don't really want. Isn't this the same thing, however? Why does it matter if I do it in a constructor with self or in a loop later? I therefore assume that the problem might be in a way I dynamically add the field to the class?
Here is the full minimal and runnable test code or whatever it is called, if you want to mess with it: http://pastebin.com/0PWnF2P0
Thank you for your time

The problem is that the value of iOption is evaluated after the
for iOption in self.option:
loops are complete. Since you reset iOption on each iteration, when the loop is completed iOption has the same value, namely the last element in self.options. You can demonstrate this at-event-time binding with the snippet:
def debug_late_bind(event):
print(iOption)
onMouseEnter(event, iOption)
for iOption in self.options:
iOption.button = Button(wrapper, text = iOption.name,
bg = '#004A7F', fg = 'white')
iOption.button.bind('<Enter>', debug_late_bind)
which will show that all events that iOption has the same value.
I split out the use of iOption to debug_late_bind to show that iOption comes in from the class scope and is not evaluated when the bind() call is executed. A more simple example would be
def print_i():
print(i)
for i in range(5):
pass
print_i()
which prints "4" because that is the last value that was assigned to i. This is why every call in your code to onMouseEnter(par_event, iOption) has the same value for iOption; it is evaluated at the time of the event, not the time of the bind. I suggest that you read up on model view controller and understand how you've tangled the view and the controller. The primary reason this has happened is that you've got two views (console and tk) which should be less coupled with the model.
Extracting the .widget property of the event is a decent workaround, but better still would be to not overwrite the scalar iOption, but instead use list of individual buttons. The code
for n, iOption in enumerate(self.options):
would help in creating a list. In your proposed workaround, you are encoding too much of the iOption model in the tkinter view. That's bound to bite you again at some point.

I don't know what the actual problem was with my original code, but I kind of just bypassed it. I added a dictionary with button as a key and option as a value and I just used the par_event.widget to get the option and it's description, which is working fine:
buttonOption = {}
def onMouseEnter(par_event):
helpLabel.configure(text = buttonOption[par_event.widget].desc)
return
def onMouseLeave(par_event):
helpLabel.configure(text = '')
return
class GUIMode(Mode):
def run(self):
#...
for iOption in self.options:
iOption.button = Button(wrapper, text = iOption.name, bg = '#004A7F', fg = 'white')
iOption.button.bind('<Enter>', lambda par_event: onMouseEnter(par_event))
iOption.button.bind('<Leave>', lambda par_event: onMouseLeave(par_event))
buttonOption[iOption.button] = iOption
#...

(no longer seeking answers) how to reset choices of a combobox in real time using wxpython?

So I'm trying to make a relatively simple TTS program using the speech module. The place I'm getting stuck at is: I want to make a list of saved text available through a combobox in the window, and if you add or delete any presets from it, it won't update the choices until the program is reloaded. Is there a way to update the choices in real time?
The combobox initializes like this:
#I have a previously set txt file with a list of presets, and its partial destination saved in a variable "savefile"
fh = open(savefile + '//presets.txt')
presets = fh.read().split('\n')
self.presetList = presets
#self.presetList is now the list of choices for the combobox, causing it to update upon loading the program
self.presetbox = wx.ComboBox(self, pos=(90, 100), size=(293, -1), choices=self.presetList, style=wx.CB_READONLY)
self.Bind(wx.EVT_COMBOBOX, self.EvtComboBox, self.presetbox)
and later on, say, to clear all choices, I would need something like this:
self.emptyList = []
self.presetbox.SetChoices(self.emptyList)
Is there a way to do this? If so that'd be great! :)

ComboBox is a mix of TextCtrl and ListBox (http://wxpython-users.1045709.n5.nabble.com/Question-on-wx-ComboBox-Clear-td2353059.html)
To reset the field, you can use self.presetbox.SetValue('')
(in case your ComboBox is not READONLY)

I'm referencing the C++ WxWidgets documentation instead of the wxPython docs, because they are usually better :), but the names should be the same.
wxComboBox derives from wxItemContainer, which has a series of functions simply called Set which you can pass in a list of strings to set the combo box contents. There are also Append and Insert functions you can use, as well as a Clear function that clears all the choices.
wxItemContainer docs are here: http://docs.wxwidgets.org/trunk/classwx_item_container.html

This worked for me, binding the EVT_COMBOBOX_DROPDOWN to update the list, than bind EVT_COMBOBOX to run a function on user's choice. That way updates, then shows the contents updated. If new choices are less, it doesn't leave the white space of the previous ones. Also you can set the combobox as READONLY to behave as a choice widget (not editable by user) as below. This code was tested under Windows, Python 3.6 and the newer wxpython (phoenix).
import wx
class Mywin(wx.Frame):
def __init__(self, parent, title):
super(Mywin, self).__init__(parent, title = title,size = (300,200))
panel = wx.Panel(self)
box = wx.BoxSizer(wx.VERTICAL)
self.label = wx.StaticText(panel,label = "Your choice:" ,style = wx.ALIGN_CENTRE)
box.Add(self.label, 0 , wx.EXPAND |wx.ALIGN_CENTER_HORIZONTAL |wx.ALL, 20)
cblbl = wx.StaticText(panel,label = "Combo box",style = wx.ALIGN_CENTRE)
box.Add(cblbl,0,wx.EXPAND|wx.ALIGN_CENTER_HORIZONTAL|wx.ALL,5)
# initial chioces are 5
#------------------------------------------------------
languages = ['C', 'C++', 'Python', 'Java', 'Perl']
#------------------------------------------------------
self.combo = wx.ComboBox(panel,choices = languages, style = wx.CB_READONLY)
box.Add(self.combo,0,wx.EXPAND|wx.ALIGN_CENTER_HORIZONTAL|wx.ALL,5)
self.combo.Bind(wx.EVT_COMBOBOX ,self.OnCombo)
self.combo.Bind(wx.EVT_COMBOBOX_DROPDOWN,self.updatelist)
panel.SetSizer(box)
self.Centre()
self.Show()
def OnCombo(self, event):
self.label.SetLabel("You selected "+self.combo.GetValue()+" from Combobox")
def updatelist(self, event):
# Chioces are now just 2
#------------------------------------------------------
OtrosLanguajes = ['C++', 'Python']
#------------------------------------------------------
self.combo.SetItems(OtrosLanguajes)
app = wx.App()
Mywin(None, 'ComboBox and Choice demo')
app.MainLoop()

The parent class of wx.ComboBox is ItemContainer.
It has the method Clear().
Use the Clear() method on the wx.ComboBox object to clear all data.