Python: QtGui.QProgressBar Color

Question

I'm wondering if there is a way to customize a color of the progress bar (QtGui.QProgressBar). Let's say we would want to make it green when bar reaches 100%.

Here is a working example:

import sys, time
from PyQt4 import QtCore, QtGui

class PbWidget(QtGui.QProgressBar):
    def __init__(self, parent=None, total=20):
        super(PbWidget, self).__init__()
        self.setMinimum(1)
        self.setMaximum(total)        
        self._active = False  

    def update_bar(self, to_add_number):
        while True:
            time.sleep(0.01)
            value = self.value() + to_add_number            
            self.setValue(value)
            QtGui.qApp.processEvents()
            if (not self._active or value >= self.maximum()):                
                break
        self._active = False

    def closeEvent(self, event):
        self._active = False


class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.main_layout = QtGui.QVBoxLayout()

        self.pb=PbWidget(total=101)
        self.main_layout.addWidget(self.pb)

        ok_button = QtGui.QPushButton("Press to update Progress Bar")
        ok_button.clicked.connect(self.OK)      
        self.main_layout.addWidget(ok_button)       

        central_widget = QtGui.QWidget()
        central_widget.setLayout(self.main_layout)
        self.setCentralWidget(central_widget)

    def OK(self):
        self.pb.update_bar(10)

if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)
    window = MainWindow()
    window.resize(480, 320)
    window.show()
    sys.exit(app.exec_())

Answer 1

Here is summary of what had been discussed so far.

It seems the easiest and most flexible way to get control over Qt widgets is to use CSS (which is well known among the web developers). CSS syntax is almost self-explanatory and easy to understand (but not to remember). Implementing CSS into Python/Pyqt is even easier. Define CSS 'styles' within .py script. Or store it as a separate myStyle.css file on disk - you would have to read it with open(path.'r') and always keep it around.

Here is an example of how CSS could be brought to control some widgets appearance (dialog box, button and progress bar) (the p.bar turns red when it reaches 51% as per RM suggestion).

---

import time
from PyQt4 import QtCore, QtGui

styleData="""
QWidget
{
    color: #b1b1b1;
    background-color: #323232;
}
QProgressBar
{
    border: 2px solid grey;
    border-radius: 5px;
    text-align: center;
}
QProgressBar::chunk
{
    background-color: #d7801a;
    width: 2.15px;
    margin: 0.5px;
}
QPushButton:pressed
{
    background-color: QLinearGradient( x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 #2d2d2d, stop: 0.1 #2b2b2b, stop: 0.5 #292929, stop: 0.9 #282828, stop: 1 #252525);
}
QComboBox:hover,QPushButton:hover
{
    border: 2px solid QLinearGradient( x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 #ffa02f, stop: 1 #d7801a);
}
QPushButton
{
    color: #b1b1b1;
    background-color: QLinearGradient( x1: 0, y1: 0, x2: 0, y2: 1, stop: 0 #565656, stop: 0.1 #525252, stop: 0.5 #4e4e4e, stop: 0.9 #4a4a4a, stop: 1 #464646);
    border-width: 1px;
    border-color: #1e1e1e;
    border-style: solid;
    border-radius: 6;
    padding: 3px;
    font-size: 12px;
    padding-left: 5px;
    padding-right: 5px;
}"""

class PbWidget(QtGui.QProgressBar):
    def __init__(self, parent=None, total=20):
        super(PbWidget, self).__init__()
        self.setMinimum(1)
        self.setMaximum(total)        
        self._active = False  

    def update_bar(self, to_add_number):
        while True:
            time.sleep(0.01)
            value = self.value() + to_add_number            
            self.setValue(value)
            if value > 50:
                self.change_color("green")
            QtGui.qApp.processEvents()
            if (not self._active or value >= self.maximum()):                
                break
        self._active = False

    def closeEvent(self, event):
        self._active = False

    def change_color(self, color):
        template_css = """QProgressBar::chunk { background: %s; }"""
        css = template_css % color
        self.setStyleSheet(css)

class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.main_layout = QtGui.QVBoxLayout()

        self.pb=PbWidget(total=101)
        self.main_layout.addWidget(self.pb)

        ok_button = QtGui.QPushButton("Press to update Progress Bar")
        ok_button.clicked.connect(self.OK)      
        self.main_layout.addWidget(ok_button)       

        central_widget = QtGui.QWidget()
        central_widget.setLayout(self.main_layout)
        self.setCentralWidget(central_widget)

    def OK(self):
        self.pb.update_bar(10)

if __name__ == '__main__':
    import sys
    app = QtGui.QApplication(sys.argv)

    window = MainWindow()
    window.resize(480, 320)
    window.setStyleSheet(styleData)  
    window.show()
    sys.exit(app.exec_())

Answer 2

Yes, use CSS for that. Yes CSS you have readed well! ;)

add this function to your PbWidget class:

def change_color(self, color):
    template_css = """QProgressBar::chunk { background: %s; }"""
    css = template_css % color
    self.setStyleSheet(css)

the color parameter expects something like: "yellow", "blue", "red" ... and also HEX notation: "#FFD45", etc ...

You can call this function inside update_bar and pass to it some color depending on the progress bar value. For example:

def update_bar(self, to_add_number):
    while True:
        time.sleep(0.5)
        value = self.value() + to_add_number            
        self.setValue(value)
        if value > 50:
            self.change_color("yellow")
        QtGui.qApp.processEvents()
        if (value >= self.maximum()):                
            break
    self._active = False

For changing others visual properties, visit: Qt StyleSheet Reference and look for QtProgressBar. Good luck!!!