import sys

from PyQt5 import QtGui
from PyQt5.QtGui import QPixmap
from PyQt5.QtWidgets import *
from PyQt5.uic import loadUi


class Main(QDialog):
    def __init__(self):
        super(Main, self).__init__()
        loadUi('uis/main.ui', self)

        self.setWindowTitle('Создание простейшей визуальной программы на Python')

        self.setWindowIcon(QtGui.QIcon('images/logo.png'))
        self.label_img.setPixmap(QPixmap('images/main.png'))
        self.label_img.setScaledContents(True)

        self.btn_solve.clicked.connect(self.solve)
        self.btn_clear.clicked.connect(self.clear)
        self.btn_exit.clicked.connect(self.exit)

    def solve(self):
        a = self.lineEdit_a.text()
        b = self.lineEdit_b.text()
        x = self.lineEdit_x.text()

        passed = validation_of_data(a, b, x)

        if passed is True:
            a = float(a)
            b = float(b)
            x = float(x)

            answer = 0.0

            if x > 6:
                answer = a / x + b / x ** 2
            else:
                answer = a ** 2 * (x + b)

            self.label_answer.setText('Ответ: ' + str(answer))
        else:
            self.label_answer.setText('Проверьте правильность введенных данных!')

    def clear(self):
        self.lineEdit_a.setText('')
        self.lineEdit_b.setText('')
        self.lineEdit_x.setText('')
        self.label_answer.setText("Ответ: ")

    def exit(self):
        self.close()


def validation_of_data(a, b, x):
    try:
        float(a)
        float(b)
        float(x)

        return True
    except Exception:
        return False


def main():
    app = QApplication(sys.argv)
    window = Main()
    window.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Python-2:
---->images
---------->logo.png
---------->main.png
---->uis
---------->main.ui
---->Main.py