pyqt5 : specific widget size

specific_widgetSize.py

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

    def initUI(self):

        grid = QGridLayout()
        self.setLayout(grid)

        names = ['Cls', 'Bck', '', 'Close',
                 '7', '8', '9', '/',
                '4', '5', '6', '*',
                 '1', '2', '3', '-',
                '0', '.', '=', '+']

        positions = [(i,j) for i in range(5) for j in range(4)]

        for position, name in zip(positions, names):
            if name == '':
                continue
            button = QPushButton(name)
            row, column = position
            if row == 2:
                button.setFixedHeight(80)
            if column == 1:
                button.setFixedWidth(50)
            grid.addWidget(button, *position)

        self.move(300, 150)
        self.setWindowTitle('Calculator')
        self.show()