text editor

import PyQt5.QtWidgets as QtW
import PyQt5.QtGui as QtG
import codecs
import re


class MainWindow(QtW.QMainWindow):
    def __init__(self):
        QtW.QMainWindow.__init__(self)
        self.setWindowTitle('My text editor')
        self.resize(700, 500)

        # New file
        self.button4 = QtW.QPushButton('New file', self)
        self.button4.clicked.connect(self.newfile)
        self.button4.setGeometry(0, 5, 60, 40)
        self.button4.show()

        # text field
        self.tab = QtW.QTextEdit(self)
        self.tab.setGeometry(0, 50, 700, 450)
        self.tab.show()

        # Open button
        self.button1 = QtW.QPushButton('Open', self)
        self.button1.clicked.connect(self.open)
        self.button1.setGeometry(70, 5, 60, 40)
        self.button1.show()

        # Save button
        self.button2 = QtW.QPushButton('Save', self)
        self.button2.clicked.connect(self.save)
        self.button2.setGeometry(140, 5, 60, 40)
        self.button2.show()

        # Exit button
        self.button3 = QtW.QPushButton('Search', self)
        self.button3.clicked.connect(self.search)
        self.button3.setGeometry(210, 5, 60, 40)
        self.button3.show()

        self.show()

    def newfile(self):
        self.tab.setText('')

    def open(self):
        filename = QtW.QFileDialog.getOpenFileName(self, 'Open file')[0]
        if not filename:
            return
        with codecs.open(filename, 'r', 'utf-8') as f:
            txt = f.read()
        self.tab.setText(txt)

    def save(self):
        filename = QtW.QFileDialog.getSaveFileName(self)[0]
        if not filename:
            return
        txt = self.tab.toPlainText()
        with codecs.open(filename, 'w', 'utf-8') as f:
            f.write(txt)

    def search(self):
        query, ok = QtW.QInputDialog.getText(self, 'Text search', u'Input text to find')
        if ok:
            text = self.tab.toPlainText()
            pattern = re.compile(query)
            word = re.search(pattern, text)
            start, end = word.span()
            self.tab.setFocus()
            self.movement(start, end)

    def movement(self, start, end):
        cursor = self.tab.textCursor()
        cursor.setPosition(start)
        cursor.movePosition(QtG.QTextCursor.Right, QtG.QTextCursor.KeepAnchor, end - start)
        self.tab.setTextCursor(cursor)


def main():
    app = QtW.QApplication([])
    window = MainWindow()
    app.exec_()


if __name__ == '__main__':
    main()