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PyQT layouts: why does QVBoxLayout stack the buttons instead of creating the layout? [duplicate]

I'm making an application in PyQt4 and this is my code so far:
import sys
from PyQt4 import QtGui, QtCore
class MainWindow(QtGui.QMainWindow):
def __init__(self):
super(MainWindow, self).__init__()
self.initUi()
def initUi(self):
self.setWindowTitle('Main Menu')
self.setFixedSize(1200, 625)
self.firstWidgets()
self.show()
def firstWidgets(self):
self.vbox1 = QtGui.QVBoxLayout()
self.task1 = QtGui.QLabel('Check 1', self)
self.task1CB = QtGui.QCheckBox(self)
self.hbox1 = QtGui.QHBoxLayout()
self.hbox1.addWidget(self.task1)
self.hbox1.addWidget(self.task1CB)
self.vbox1.addLayout(self.hbox1)
self.setLayout(self.vbox1)
def main():
application = QtGui.QApplication(sys.argv)
gui = MainWindow()
sys.exit(application.exec_())
if __name__=='__main__':
main()
My problem is in MainWindow.firstWidgets(). I try to set a layout but I get an error even though that's my first time using .setLayout for that form, which confuses me.
QWidget::setLayout: Attempting to set QLayout "" on MainWindow "",
which already has a layout

You can't set a QLayout directly on the QMainWindow. You need to create a QWidget and set it as the central widget on the QMainWindow and assign the QLayout to that.
wid = QtGui.QWidget(self)
self.setCentralWidget(wid)
layout = QtGui.QVBoxLayout()
wid.setLayout(layout)
NOTE: This is for Qt4 -- see the other answer on this question for the Qt5 updated code.

Just an update to Brenden Abel's answer:
QWidget and QVBoxLayout (for Python3, PyQt5) are now contained in the PyQt5.QtWidgets module and not the PyQt5.QtGui module.
So updated code:
wid = QtWidgets.QWidget(self)
self.setCentralWidget(wid)
layout = QtWidgets.QVBoxLayout()
wid.setLayout(layout)

This is an example using PyQt5
import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication, QMainWindow, QVBoxLayout, QPushButton, QWidget
class MainWindow(QMainWindow):
def __init__(self):
super().__init__()
self.setWindowTitle('My App')
# Cannot set QxxLayout directly on the QMainWindow
# Need to create a QWidget and set it as the central widget
widget = QWidget()
layout = QVBoxLayout()
b1 = QPushButton('Red' ); b1.setStyleSheet("background-color: red;")
b2 = QPushButton('Blue' ); b2.setStyleSheet("background-color: blue;")
b3 = QPushButton('Yellow'); b3.setStyleSheet("background-color: yellow;")
layout.addWidget(b1)
layout.addWidget(b2)
layout.addWidget(b3)
widget.setLayout(layout)
self.setCentralWidget(widget)
def main():
app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())
if __name__ == '__main__':
main()

How can I position widgets inside a layout?

I'm having trouble with spacing widgets in a QVboxlayout. I have this code:
from PyQt5 import QtGui, QtWidgets, QtCore
from PyQt5.QtWidgets import QApplication, QMainWindow
import sys
class MainWindow(QMainWindow):
def __init__(self):
super(MainWindow, self).__init__()
win_w, win_h = 250, 1
self.setGeometry((1920 - win_w) // 2, (1080 - win_h) // 2, win_w, win_h)
self.setWindowTitle('Test')
self.setFont(QtGui.QFont('Times', 12))
self.central_widget()
def central_widget(self):
widget = QtWidgets.QWidget()
grid = QtWidgets.QGridLayout()
group_box1 = QtWidgets.QGroupBox('Group Box')
v1 = QtWidgets.QVBoxLayout()
text_edit1 = QtWidgets.QTextEdit()
v1.addWidget(QtWidgets.QPushButton('Button'))
v1.addWidget(text_edit1)
group_box1.setLayout(v1)
grid.addWidget(group_box1, 0, 0)
widget.setLayout(grid)
self.setCentralWidget(widget)
if __name__ == '__main__':
app = QApplication(sys.argv)
win = MainWindow()
win.show()
sys.exit(app.exec_())
Running this brings up this window:
Adding this line v1.setSpacing(100) changes it to this:
Is there any way to make it add the spacing horizontally? Like this:

Use the alignment keyword argument for addWidget():
v1.addWidget(QtWidgets.QPushButton('Button'), alignment=QtCore.Qt.AlignRight)
As already suggested, you should carefully read the documentation about layout managers, including all the listed QLayout subclasses and all their methods. You can do some experiments on your own with them also in Designer, so that you can better understand how they work by directly seeing the results.

Put a QToolBar in a QWidget instead of QMainWindow

I am trying to put a QToolBar on a layout of a QWidget instead of QMainWindow. On QMainWindow and QWidget is working fine, but when i try to add it on a layout first, is not. Am I doing something wrong? Is it possible? Here is my code:
from PyQt4 import QtGui, QtCore
import sys
img = '../../Images/logo.png'
if __name__ == '__main__':
app = QtGui.QApplication(sys.argv)
mainWin = QtGui.QMainWindow()
widget = QtGui.QWidget()
hLayout = QtGui.QHBoxLayout()
'''ToolBar On main Window '''
basicToolBar = mainWin.addToolBar('Basic')
basicToolBar.addAction(QtGui.QAction('Test', mainWin))
# basicToolBar.addAction(QtGui.QAction(QtGui.QIcon(img), 'Test', mainWin))
# mainWin.show()
'''ToolBar On Widget '''
# Case 1: Set widget as parent
# widgetToolBar = QtGui.QToolBar(widget)
# widgetToolBar.addAction(QtGui.QAction('Test', widget))
# widgetToolBar.addAction(QtGui.QAction(QtGui.QIcon(img), QtGui.QAction('Test', widget))
# Case 2: Set toolBat on a layout
widgetToolBar = QtGui.QToolBar()
widgetToolBar.addAction(QtGui.QAction('Test', None))
# widgetToolBar.addAction(QtGui.QAction(QtGui.QIcon(img), 'Test', None))
hLayout.addWidget(widgetToolBar)
widget.setLayout(hLayout)
widget.show()
# Run
sys.exit(app.exec_())

QToolBar can only be in a QMainWindow since the QMainWindow has a special layout.
So you can use a secondary QMainWindow without problems as I show below:
from PyQt4 import QtCore, QtGui
class MainWindow(QtGui.QMainWindow):
def __init__(self, parent=None):
super(MainWindow, self).__init__(parent)
self.tabwidget = QtGui.QTabWidget()
self.setCentralWidget(self.tabwidget)
for name in ("tab1", "tab2", "tab3"):
self.create_widgets(name)
def create_widgets(self, name):
w = QtGui.QMainWindow()
self.tabwidget.addTab(w, name)
basicToolBar = w.addToolBar('Basic')
basicToolBar.addAction('Test')
basicToolBar.addAction(QtGui.QIcon("home.png"), 'Test')
tab = QtGui.QTabWidget()
w.setCentralWidget(tab)
for i in range(10):
tab.addTab(QtGui.QWidget(), "tab-{}".format(i))
if __name__ == '__main__':
import sys
app = QtGui.QApplication(sys.argv)
w = MainWindow()
w.show()
sys.exit(app.exec_())

Hmmm have you read the description of QToolBar? http://doc.qt.io/qt-5/qtoolbar.html#details
I think it won't work like this if your Object isn't a child of QMainWindow. The documentation says:
When a QToolBar is not a child of a QMainWindow, it loses the ability to populate the extension pop up with widgets added to the toolbar using addWidget(). Please use widget actions created by inheriting QWidgetAction and implementing QWidgetAction::createWidget() instead.

PyQt5: Want to start a specific subprocess with a button click

One day old in terms of experience with PyQT, I followed sample code HERE to do this, but I am clueless as to how I could separate the start download part from the start GUI part, so that I can instead start that when I press the OK (startBtn)button. Also, know the command I do doesn't do anything but give you an error, but I know that works.
Any help appreciated!
from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow, QAction, qApp, QDesktopWidget, QPushButton, QHBoxLayout, QVBoxLayout, QTextEdit
from PyQt5.QtGui import QIcon
from PyQt5.QtCore import QThread, QProcess
import sys
class GUI(QProcess):
def __init__(self):
super().__init__()
# Create an instance variable here (of type QTextEdit)
startBtn = QPushButton('OK')
stopBtn = QPushButton('Cancel')
#startBtn.clicked.connect()
stopBtn.clicked.connect(qApp.exit)
self.hbox = QHBoxLayout()
self.hbox.addStretch(1)
self.hbox.addWidget(startBtn)
self.hbox.addWidget(stopBtn)
self.edit = QTextEdit()
self.edit.setWindowTitle("QTextEdit Standard Output Redirection")
self.vbox = QVBoxLayout()
self.vbox.addStretch(1)
self.vbox.addWidget(self.edit)
self.vbox.addLayout(self.hbox)
#setLayout(self.vbox)
self.central=QWidget()
#self.vbox.addWidget(self.edit)
self.central.setLayout(self.vbox)
self.central.show()
def readStdOutput(self):
self.edit.append(str(self.readAllStandardOutput()))
def main():
app = QApplication(sys.argv)
qProcess = GUI()
qProcess.setProcessChannelMode(QProcess.MergedChannels);
qProcess.start("youtube-dl")
qProcess.readyReadStandardOutput.connect(qProcess.readStdOutput);
return app.exec_()
if __name__ == '__main__':
main()
2 notes:
If you also know how to disable the OK button when you press it, until the process is finished, then I'd love to know.
Not all imports are used, but I can clean that later. PyCharm show which is used and not. Cleanup is for later.

To do what you ask you have to have some considerations:
youtube-dl requires parameters, like the url, for this I have placed a QLineEdit.
To know when the process starts and ends, we use the signal: stateChanged(newState)
Complete code:
import sys
from PyQt5.QtCore import QProcess
from PyQt5.QtWidgets import QApplication, QWidget, QPushButton, QHBoxLayout, QVBoxLayout, QTextEdit, QLabel, QLineEdit
class GUI(QProcess):
def __init__(self, parent=None):
super(GUI, self).__init__(parent=parent)
# Create an instance variable here (of type QTextEdit)
self.startBtn = QPushButton('OK')
self.stopBtn = QPushButton('Cancel')
self.hbox = QHBoxLayout()
self.hbox.addStretch(1)
self.hbox.addWidget(self.startBtn)
self.hbox.addWidget(self.stopBtn)
self.label = QLabel("Url: ")
self.lineEdit = QLineEdit()
self.lineEdit.textChanged.connect(self.EnableStart)
self.hbox2 = QHBoxLayout()
self.hbox2.addWidget(self.label)
self.hbox2.addWidget(self.lineEdit)
self.edit = QTextEdit()
self.edit.setWindowTitle("QTextEdit Standard Output Redirection")
self.vbox = QVBoxLayout()
self.vbox.addStretch(1)
self.vbox.addLayout(self.hbox2)
self.vbox.addWidget(self.edit)
self.vbox.addLayout(self.hbox)
self.central = QWidget()
self.central.setLayout(self.vbox)
self.central.show()
self.startBtn.clicked.connect(self.startDownload)
self.stopBtn.clicked.connect(self.kill)
self.stateChanged.connect(self.slotChanged)
self.EnableStart()
def slotChanged(self, newState):
if newState == QProcess.NotRunning:
self.startBtn.setDisabled(False)
elif newState == QProcess.Running:
self.startBtn.setDisabled(True)
def startDownload(self):
self.start("youtube-dl", [self.lineEdit.text()])
def readStdOutput(self):
self.edit.append(str(self.readAllStandardOutput()))
def EnableStart(self):
self.startBtn.setDisabled(self.lineEdit.text() == "")
def main():
app = QApplication(sys.argv)
qProcess = GUI()
qProcess.setProcessChannelMode(QProcess.MergedChannels)
qProcess.readyReadStandardOutput.connect(qProcess.readStdOutput)
return app.exec_()
if __name__ == '__main__':
main()
Screenshot:

Qt Multiple GraphicsEffects

Is there a way in Qt5 to apply a QGraphicsEffect to a widget, even when one of its parent widgets already has a QGraphicsEffect applied to it?
When i try the following:
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *
from PyQt5.QtCore import *
import sys
class ParentWidget(QWidget):
def __init__(self,parent):
super().__init__(parent)
effect = QGraphicsBlurEffect(self)
self.setGraphicsEffect(effect)
effect.setBlurRadius(0)
class ChildWidget(ParentWidget):
def __init__(self,parent):
super().__init__(parent)
self.layout = QGridLayout(self)
widget = QWidget()
widget.setObjectName('reviewControlArea')
effect = QGraphicsOpacityEffect(widget)
widget.setGraphicsEffect(effect)
self.layout.addWidget(widget)
if __name__ == "__main__":
app = QApplication(sys.argv)
MainWindow = QMainWindow()
cw = ChildWidget(MainWindow)
MainWindow.setCentralWidget(cw)
MainWindow.show()
sys.exit(app.exec_())
The stdout says:
QPainter::begin: A paint device can only be painted by one painter at a time.