Trouble Understanding Signal Mapper PyQt - python

So I am generating a menu of options based on some files on my system. I have a list list of objects I need to dynamically generate an option in the menu for and need to be able to let the function that is doing the creation know which object to use. After some research I found the post below. I could not comment as my rep is not high yet: How to pass arguments to callback functions in PyQt
When I run this the signal mapper is not working right. It is not even calling the handleButton correctly. Any ideas as to how to use the signal mapper correctly?
from PyQt4 import QtGui, QtCore
class Window(QtGui.QMainWindow):
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.mapper = QtCore.QSignalMapper(self)
self.toolbar = self.addToolBar('Foo')
self.toolbar.setToolButtonStyle(QtCore.Qt.ToolButtonTextOnly)
for text in 'One Two Three'.split():
action = QtGui.QAction(text, self)
self.mapper.setMapping(action, text)
action.triggered.connect(self.mapper.map)
self.toolbar.addAction(action)
self.mapper.mapped['QString'].connect(self.handleButton)
self.edit = QtGui.QLineEdit(self)
self.setCentralWidget(self.edit)
def handleButton(self, identifier):
print 'run'
if identifier == 'One':
text = 'Do This'
print 'Do One'
elif identifier == 'Two':
text = 'Do That'
print 'Do Two'
elif identifier == 'Three':
print 'Do Three'
text = 'Do Other'
self.edit.setText(text)
if __name__ == '__main__':
import sys
app = QtGui.QApplication(sys.argv)
window = Window()
window.resize(300, 60)
window.show()
sys.exit(app.exec_())
EDIT:
I've found that by using old-style signal/slot connections this is fixed:
#action.triggered.connect(self.mapper.map)
self.connect(action, QtCore.SIGNAL("triggered()"), self.mapper, QtCore.SLOT("map()"))
and
#self.mapper.mapped['QString'].connect(self.handleButton)
self.connect(self.mapper, QtCore.SIGNAL("mapped(const QString &)"), self.handleButton)
Am I using the new-style connections incorrectly?
Based on this post as well as the original link I posted, I thought I was doing things correctly.

The original example code (which I wrote), works perfectly fine for me using either Python2 or Python3 with several different recent versions of PyQt4. However, if I use a really old version of PyQt4 (4.7), the handler no longer gets called.
The reason (and solution) for this is given in the response to the mailing list post you linked to:
It's actually a problem with QSignalMapper.map() being called from a
proxy rather than new-style connections.
The workaround is to explicitly specify a signal that is compatible
with map()...
self.b1.clicked[()].connect(self.mapper.map)
Tonight's PyQt snapshot will be smarter about finding a usable Qt slot
before deciding that it needs to use a proxy so that the workaround
won't be necessary.
There are some signals (like clicked and triggered) which always send a default value unless you explicitly request otherwise. With the old-style signals, you can specify the no default overload it with SIGNAL("triggered()"), but with new-style signals, you have to do it like this:
action.triggered[()].connect(self.mapper.map)
But that is only necessary with very old versions of PyQt4 - the underlying issue was fixed back in 2010 (don't know the exact version, but 4.8 should be okay).

Related

Handling QDialog's events safely in PyQT

I'm having troubles with a Qt Application (managed through PyQt5) which used to be reliable, until a bunch of updates (where I ended up with PyQt6). PyQt6 is not the culprit here, as I began to have those problems with later PyQt5 versions.
I'm suspecting my problems are instead linked to an abuse of exec() methods call. The full traceback is not available (I've only a RuntimeError with a cryptic message telling me the Dialog is not available anymore); what (I think) I'm seeing are the parent windows randomly disappearing. This behaviour is indeed mentionned in the Qt documentation:
Note: Avoid using this function; instead, use open(). Unlike exec(), open() is asynchronous, and does not spin an additional event loop. This prevents a series of dangerous bugs from happening (e.g. deleting the dialog's parent while the dialog is open via exec()). When using open() you can connect to the finished() signal of QDialog to be notified when the dialog is closed.
Initially, my app was constructed this way:
QMainWindow A > QDialog B > QDialog C > ...
Each QDialog was launched using .exec() method.
The pseudo code could be summarized this way [edit] :
class A(QMainWindow):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.ui = Some_Ui_From_QtDesigner()
self.ui.setupUi(self)
self.ui.some_menu.triggered.connect(self.load_popup)
def load_popup():
B = QDialog(A)
if B.exec() == 1:
# Do some things (extract data from B and update A)
if C.exec() == 1:
# Do some things (extract data from C and update B)
qApp = QtWidgets.QApplication.instance()
a = A()
a.show()
qApp.setQuitOnLastWindowClosed(True)
qApp.exec()
I've tried to use .open() methods instead of .exec() and came up with something like this (using QLoopEvent's and events handling):
def process_C_qdialog(parent):
C = QDialog(parent)
# Construct your QDialog some more ...
loop = QtCore.QEventLoop()
my_result = None
def _accept():
my_result = "blah"
loop.exit(0)
def _reject():
loop.exit(-1)
f.accepted.connect(_accept)
f.rejected.connect(_reject)
f.open()
loop.exec()
return my_result
My troubles are far from over as yet. I suspect that recreating manually a QEventLoop causes the same problems than using .exec() in the first place.
So some questions:
Am I right about the QEventLoop?
Would it be safer/enough to leave the parent out of the QDialog generator?
Any advice on how to handle this the right way (keeping a modal dialog if possible)?
More generally, are they any safe ways to reproduce the static methods of Qt through a custom python function? (ie, a function which would load a customized popup, wait for the user's input and returning it)
Note: as this behaviour happens erratically (and without the full traceback available), I'm not 100% sure of this; but I suspect that even a simple QMessageBox().exec() has the same effects, even if this is not stated in the doc.

How to create an interactive text menu in Python?

I'm not sure what to call it. I want to know how to make one of those menus where you use the arrow keys to highlight your options and press enter to accept it.
The questioner acknowledged being unsure how to clearly state what they're after (I know the feeling!) and it is a little while after the question was posted, but in light of their comment suggesting they were after text, I believe something like python-prompt-toolkit, which is used to provide text-based autocomplete in a number of Python projects, may offer a solution.
There is documentation here which has this example of using a WordCompleter:
from prompt_toolkit import prompt
from prompt_toolkit.completion import WordCompleter
html_completer = WordCompleter(['<html>', '<body>', '<head>', '<title>'])
text = prompt('Enter HTML: ', completer=html_completer)
print('You said: %s' % text)
That produces output like this:
The example above is still relatively like a ComboBox merely rendered in text, but there are ways to produce other styles of menu as shown in the gallery here.
If that isn't sufficient then another option is looking into something that wraps ncurses, like https://bitbucket.org/npcole/npyscreen or http://urwid.org/ .
The answer to your question including the examples you provided is curses. This package is very much dependent on the underlying operating system. So if platform independence is key then you will get issues. There is for example a Windows port UniCurses but your implementation has to handle this switch if necessary.
There are also tools built on top of curses. Four example Urwid.
I personally have some experience with curses and if you have Linux as the underlying system this can be fun if your requirements are robust and simple. Like your menu requirement. I have to say though that the learning curve is pretty steep.
Hope this helps. But given the broad question thus is the only level of detail to provide at this stage.
I think you mean Combobox.
Here is a short example based on this and PyQt:
from PyQt4 import QtGui, QtCore
import sys
class CheckableComboBox(QtGui.QComboBox):
def __init__(self):
super(CheckableComboBox, self).__init__()
self.view().pressed.connect(self.handleItemPressed)
self.setModel(QtGui.QStandardItemModel(self))
def handleItemPressed(self, index):
item = self.model().itemFromIndex(index)
if item.checkState() == QtCore.Qt.Checked:
item.setCheckState(QtCore.Qt.Unchecked)
else:
item.setCheckState(QtCore.Qt.Checked)
class Dialog_01(QtGui.QMainWindow):
def __init__(self):
super(QtGui.QMainWindow,self).__init__()
myQWidget = QtGui.QWidget()
myBoxLayout = QtGui.QVBoxLayout()
myQWidget.setLayout(myBoxLayout)
self.setCentralWidget(myQWidget)
self.toolbutton = QtGui.QToolButton(self)
self.toolbutton.setText('Select Categories ')
self.toolmenu = QtGui.QMenu(self)
for i in range(3):
action = self.toolmenu.addAction("Category " + str(i))
action.setCheckable(True)
self.toolbutton.setMenu(self.toolmenu)
self.toolbutton.setPopupMode(QtGui.QToolButton.InstantPopup)
myBoxLayout.addWidget(self.toolbutton)
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
combo = Dialog_01()
combo.show()
combo.resize(480,320)
sys.exit(app.exec_())

pyqt: A correct way to connect multiple signals to the same function in pyqt (QSignalMapper not applicable)

I've ready many posts on how to connect multiple signals to the same event handler in python and pyqt. For example, connecting several buttons or comboboxes to the same function.
Many examples show how to do this with QSignalMapper, but it is not applicable when the signal carries a parameter, as with combobox.currentIndexChanged
Many people suggest it can be made with lambda. It is a clean and pretty solution, I agree, but nobody mentions that lambda creates a closure, which holds a reference - thus the referenced object can not be deleted. Hello memory leak!
Proof:
from PyQt4 import QtGui, QtCore
class Widget(QtGui.QWidget):
def __init__(self):
super(Widget, self).__init__()
# create and set the layout
lay_main = QtGui.QHBoxLayout()
self.setLayout(lay_main)
# create two comboboxes and connect them to a single handler with lambda
combobox = QtGui.QComboBox()
combobox.addItems('Nol Adyn Dwa Tri'.split())
combobox.currentIndexChanged.connect(lambda ind: self.on_selected('1', ind))
lay_main.addWidget(combobox)
combobox = QtGui.QComboBox()
combobox.addItems('Nol Adyn Dwa Tri'.split())
combobox.currentIndexChanged.connect(lambda ind: self.on_selected('2', ind))
lay_main.addWidget(combobox)
# let the handler show which combobox was selected with which value
def on_selected(self, cb, index):
print '! combobox ', cb, ' index ', index
def __del__(self):
print 'deleted'
if __name__ == '__main__':
import sys
app = QtGui.QApplication(sys.argv)
wdg = Widget()
wdg.show()
wdg = None
sys.exit(app.exec_())
The widget is NOT deleted though we clear the reference. Remove the connection to lambda - it gets deleted properly.
So, the question is: which is the proper way to connect several signals with parameters to a single handler without leaking memory?
It is simply untrue that an object cannot be deleted because a signal connection holds a reference in a closure. Qt will automatically remove all signal connections when it deletes an object, which will in turn remove the reference to the lambda on the python side.
But this implies that you cannot always rely on Python alone to delete objects. There are two parts to every PyQt object: the Qt C++ part, and the Python wrapper part. Both parts must be deleted - and sometimes in a specific order (depending on whether Qt or Python currently has ownership of the object). In addition to that, there's also the vagaries of the Python garbage-collector to factor in (especially during the short period when the interpreter is shutting down).
Anyway, in your specific example, the easy fix is to simply do:
# wdg = None
wdg.deleteLater()
This schedules the object for deletion, so a running event-loop is required for it have any effect. In your example, this will also automatically quit the application (because the object is the last window closed).
To more clearly see what's happening, you can also try this:
#wdg = None
wdg.deleteLater()
app.exec_()
# Python part is still alive here...
print(wdg)
# but the Qt part has already gone
print(wdg.objectName())
Output:
<__main__.Widget object at 0x7fa953688510>
Traceback (most recent call last):
File "test.py", line 45, in <module>
print(wdg.objectName())
RuntimeError: wrapped C/C++ object of type Widget has been deleted
deleted
EDIT:
Here's another debugging example that hopefully makes it even clearer:
wdg = Widget()
wdg.show()
wdg.deleteLater()
print 'wdg.deleteLater called'
del wdg
print 'del widget executed'
wd2 = Widget()
wd2.show()
print 'starting event-loop'
app.exec_()
Output:
$ python2 test.py
wdg.deleteLater called
del widget executed
starting event-loop
deleted
in many cases the parameter carried by signal can be catched in another way, e.g. if an objectName is set for the sending object, so QSignalMapper can be used:
self.signalMapper = QtCore.QSignalMapper(self)
self.signalMapper.mapped[str].connect(myFunction)
self.combo.currentIndexChanged.connect(self.signalMapper.map)
self.signalMapper.setMapping(self.combo, self.combo.objectName())
def myFunction(self, identifier):
combo = self.findChild(QtGui.QComboBox,identifier)
index = combo.currentIndex()
text = combo.currentText()
data = combo.currentData()

Overriding/Reimplementing Slots in PySide

I have almost the exact same question as the one found here:
Override shouldInterruptJavaScript in QWebPage with PySide
In my case though I want to override the copy and paste slots on QLineEdit
import sys
from PySide import QtGui, QtCore
class myLineEdit(QtGui.QLineEdit):
# FIXME: This is not working, the slot is not overriden!
#QtCore.Slot()
def copy(self):
print 'overridden copy event'
App.clipboard().setText('customized text')
return False
#QtCore.Slot()
def paste(self):
print 'overridden paste event'
self.setText('customized text')
return False
if __name__ == "__main__":
App = QtGui.QApplication(sys.argv)
Widget = myLineEdit()
Widget.show()
cmenu = Widget.createStandardContextMenu()
sys.exit(App.exec_())
I'm using Python 2.7.3, with PySide 1.2.2
I don't know if these methods are even supposed to be override-able, but I can't find any documentation that says they shouldn't be.
I also found this page
http://qt-project.org/faq/answer/is_it_possible_to_reimplement_non-virtual_slots
The page explains how certain kinds of slots get pointers set to them by functions that get called when the object is initialized (or something along those lines, I'm not as familiar with the C++).
Following this logic I added the createStandardContextMenu() call above in the hopes that it would reinitialize the slots for at least the context menu, but no luck.
Am I doing something wrong? Or should I try filing a bug report?
You cannot override QLineEdit.copy or QLineEdit.paste in such a way that they will be called internally by Qt.
In general, you can only usefully override or reimplement Qt functions that are defined as being virtual. The Qt Docs will always specify whether this is the case, and for QLineEdit, there are no public slots that are defined in that way.
There is also no easy workaround. There are a lot of different ways in which copy and paste operations (or their equivalents) can be invoked, such as keyboard shortcuts, context menu, drag and drop, etc. It can be done: but it's a lot of work to get complete control over all these sorts of operations. So you need to think carefully about what you're trying to achieve before deciding how to proceed.

Lock a choice in PyQt4 QComboBox using a QCheckBox

I am beginning to write a GUI using PyQt4. This is my first experience with GUIs (and also oo-programming is somewhat new to me). Part of that GUI will be like 4 to 5 instances of QComboBox. As many choices are to be made, I want the user to be able to lock a choice, such that is not being changed unintenionally later. For one QComboBox I can solve the problem with this code that I wrote:
import sys
from PyQt4 import QtGui, QtCore
class MyGui(QtGui.QWidget):
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.resize(250, 50)
# vertical layout for widgets
self.vbox = QtGui.QVBoxLayout()
self.setLayout(self.vbox)
# Create a combo box with some choices
self.combo_color = QtGui.QComboBox()
self.vbox.addWidget(self.combo_color)
items = 'Red Yellow Purple'.split()
self.combo_color.addItems(items)
self.connect(self.combo_color, QtCore.SIGNAL('activated(QString)'), self.use_choice)
# add a checkbox next to the combobox which (un-)locks the the combo-choice
self.checkbox_color = QtGui.QCheckBox('Lock Choice', self)
self.vbox.addWidget(self.checkbox_color)
self.connect(self.checkbox_color, QtCore.SIGNAL('stateChanged(int)'), self.lock_choice)
def use_choice(self, text):
# do something very useful with the choice
print 'The current choice is: {choice}'.format(choice=text)
def lock_choice(self):
if self.checkbox_color.isChecked():
self.combo_color.setEnabled(False)
print 'Choice {choice} locked'.format(choice=self.combo_color.currentText())
else:
self.combo_color.setEnabled(True)
print 'Choice unlocked'
if __name__ == "__main__":
app = QtGui.QApplication(sys.argv)
mygui = MyGui()
mygui.show()
app.exec_()
This code does what it should, but I am very unhappy with its design, because the method lock_choice is hard-coded to only lock the choice of the QComboBox combo_color. What if I now want to do the same thing for another QComboBox (say combo_name) and a second QCheckBox (say checkbox_name) which could be realized by appending the following code to the classes __init__(self) code block:
# create second combo box with some other choices
self.combo_name = QtGui.QComboBox()
self.vbox.addWidget(self.combo_name)
items = 'Bob Peter'.split()
self.combo_name.addItems(items)
self.connect(self.combo_name, QtCore.SIGNAL('activated(QString)'), self.use_choice)
# add a checkbox next to the combobox which (un-)locks the the combo-choice
self.checkbox_name = QtGui.QCheckBox('Lock Choice', self)
self.vbox.addWidget(self.checkbox_name)
self.connect(self.checkbox_name, QtCore.SIGNAL('stateChanged(int)'), self.lock_choice) # <-- obviously wrong, as it (un-)locks color choice at the moment
Both QComboBoxes can share the method use_choice() right now, but they cannot share the method lock_choice(), as both checkboxes lock the color-choice. I want the checkbox checkbox_name to lock the name-choice, without copy and pasting the current lock_choice()-method and switching the hardcoded combobox.
I am sure there is an easy way, like passing the target-combobox to the method, which i just don't know yet. Help would be appreciated!
Try partial functions-
from functools import partial
with the connect signal, pass the QWidget name:
self.connect(self.checkbox_color, QtCore.SIGNAL('stateChanged(int)'), partial(self.lock_choice, self.combo_color))
And in your method, you may add an argument.
We'll add an argument in the method like below, to handle the QWidget(QComboBox) that we'll pass through the partial function above.
def lock_choice(self, combos):
if combos.isEnabled(True):
combos.setEnabled(False)
print 'Choice {choice} locked'.format(choice=combos.currentText())
The simplest solution would be to use the toggled signal with the setDisabled slot:
self.checkbox_color.toggled.connect(self.combo_color.setDisabled)
(And note how much cleaner the new-style sytax is when making signal connections).
It's also worth pointing out that you can also use a lambda for making inline signal connections, like this:
self.checkbox_color.toggled.connect(
lambda checked: self.combo_color.setDisabled(checked))
This is probably the most idiomatic solution when there are no convenient signal/slot pairings (and of course partial functions can achieve more or less the same thing in different way).

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