import sys
from PyQt5 import QtCore, QtWidgets

class Example(QtWidgets.QWidget):
    def __init__(self):
        super(Example, self).__init__()
        self.initUI()

    def initUI(self):     
        hbox = QtWidgets.QHBoxLayout(self)

        left = QtWidgets.QFrame(self)       
        left.setFrameShape(QtWidgets.QFrame.StyledPanel)

        mid = QtWidgets.QFrame(self)
        mid.setFrameShape(QtWidgets.QFrame.StyledPanel)

        right = QtWidgets.QFrame(self)
        right.setFrameShape(QtWidgets.QFrame.StyledPanel)

        splitter = QtWidgets.QSplitter(QtCore.Qt.Horizontal)
        splitter.addWidget(left)
        splitter.addWidget(mid)
        splitter.addWidget(right)
        splitter.setStretchFactor(1, 1)
        splitter.setSizes([250, 640, 250])

        hbox.addWidget(splitter)
        self.setLayout(hbox)

        QtWidgets.QApplication.setStyle(QtWidgets.QStyleFactory.create('Cleanlooks'))
        self.resize(500+640, 700)
        self.setWindowTitle('QtGui.QSplitter')
        self.show()

def main():
    app = QtWidgets.QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()