import sys
from PyQt5.QtWidgets import *
from PyQt5 import QtGui, QtWidgets
from PyQt5.QtCore import *

class Button(QPushButton):
    def __init__(self, text, parent):
        super().__init__(text, parent=parent or None)
        self.setSizePolicy ( QSizePolicy.Expanding, QSizePolicy.Expanding)

class App(QMainWindow):

    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        leftpanel = QTreeView()
        rightpanel = QTreeView()

        boxes = QGridLayout()
        boxes.addWidget(leftpanel, 0,0)
        boxes.addWidget(rightpanel, 0,1)

        mainlayout = QVBoxLayout()
        mainlayout.addLayout(boxes)
        mainlayout.addWidget(QComboBox())
        mainlayout.addWidget(QPushButton('Kopiuj'))

        buttons = QGridLayout()
        for i, t in enumerate (['F3 - Podgląd', 'F4 - Edycja']):
            buttons.addWidget(QPushButton(t), 0,i)

        mainlayout.addLayout(buttons)

        window = QWidget()
        window.setLayout(mainlayout)

        self.setCentralWidget(window)
        self.setWindowTitle('Total Commander')
        self.setGeometry(300, 300, 350, 250)
        self.statusBar().showMessage('Podaj cyfrę/liczbę')
        self.show()

if __name__ == '__main__':

    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())