from PyQt5 import QtWidgets
from w import W
import sys

class D(QtWidgets.QDialog):
    def __init__(self):
        super(D, self).__init__()

        self.btn = QtWidgets.QPushButton('Click me')

        layout = QtWidgets.QHBoxLayout()
        layout.addWidget(self.btn)

        self.setLayout(layout)

        self.btn.clicked.connect(self.runWin)

    def runWin(self):
        win = W('Test')
        win.show()
        self.close()

if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    login = D()
    login.show()
    app.exec()