Python NameError: global name 'Form' is not defined pyqt

Question

I am trying to design Garage App. The app has two options (Sign IN, Sign Up) and this Widget called 'Welcome Window' when user chooses Sign IN.

The program should close 'Welcome Window' and open anther widget called 'Log In', then the 'Log In' widget has two push buttons: 'Ok' and 'Back'. When the user presses 'Back', it should Close 'Log In' widget and reopen 'Welcome Window'. But it open 'Welcome window' without close 'Login window' and raises the error

NameError: global name 'Form' is not defined code of 'WelcomeWidget'

from PyQt4 import QtCore, QtGui
import SignIN

try:
     _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
     def _fromUtf8(s):
         return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, 
_encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_Form(object):
    def SignINF(self):
        self.SignINWindow = QtGui.QWidget()
        self.ui = SignIN.Ui_Form()
        self.ui.setupUi(self.SignINWindow)
        self.SignINWindow.show()
        Form.close()
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(500, 360)
        Form.setStyleSheet(_fromUtf8("background-image: 
url(:/img/Screenshot from 2017-09-20 17-37-17.png);"))
        self.pushButton_2 = QtGui.QPushButton(Form)
        self.pushButton_2.setGeometry(QtCore.QRect(120, 290, 75, 31))
        self.pushButton_2.setStyleSheet(_fromUtf8("color: rgb(255, 
255, 255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.pushButton_2.setObjectName(_fromUtf8("pushButton_2"))
        self.pushButton_2.clicked.connect(self.SignINF)
        self.pushButton = QtGui.QPushButton(Form)
        self.pushButton.setGeometry(QtCore.QRect(29, 291, 75, 31))
        self.pushButton.setStyleSheet(_fromUtf8("color: rgb(255, 255, 
255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.label = QtGui.QLabel(Form)
        self.label.setGeometry(QtCore.QRect(30, 50, 458, 34))
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("DejaVu Serif"))
        font.setPointSize(22)
        font.setBold(False)
        font.setItalic(False)
        font.setWeight(9)
        self.label.setFont(font)
        self.label.setStyleSheet(_fromUtf8("color: rgb(255, 255, 
255);\n"
"font: 75 22pt \"DejaVu Serif\";\n"
""))
        self.label.setObjectName(_fromUtf8("label"))
        self.label_2 = QtGui.QLabel(Form)
        self.label_2.setGeometry(QtCore.QRect(360, 330, 131, 20))
        self.label_2.setStyleSheet(_fromUtf8("color: rgb(255, 255, 
255);\n"
"font: 63 italic 10pt \"URW Chancery L\";"))
        self.label_2.setObjectName(_fromUtf8("label_2"))

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(_translate("Form", "Form", None))
        self.pushButton_2.setText(_translate("Form", "Sign In", None))
        self.pushButton.setText(_translate("Form", "Sign Up", None))
        self.label.setText(_translate("Form", "Welcome To Our Smart 
Garage", None))
        self.label_2.setText(_translate("Form", "Power By AIET 
Students", None))

import iamge_rc

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Form = QtGui.QWidget()
    ui = Ui_Form()
    ui.setupUi(Form)
    Form.show()
    sys.exit(app.exec_())

Code for 'Sign In Widget'

from PyQt4 import QtCore, QtGui
import WelFrame

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_Form(object):
    def Back(self):
        self.WelcomWindow = QtGui.QWidget()
        self.ui = WelFrame.Ui_Form()
        self.ui.setupUi(self.WelcomWindow)
        self.WelcomWindow .show()
        Form.close()
    def setupUi(self, Form):
        Form.setObjectName(_fromUtf8("Form"))
        Form.resize(500, 360)
        Form.setStyleSheet(_fromUtf8("background-image: url(:/img/Screenshot from 2017-09-20 17-37-17.png);"))
        self.gridLayout = QtGui.QGridLayout(Form)
        self.gridLayout.setObjectName(_fromUtf8("gridLayout"))
        self.label = QtGui.QLabel(Form)
        self.label.setStyleSheet(_fromUtf8("color: rgb(255, 255, 255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.label.setObjectName(_fromUtf8("label"))
        self.gridLayout.addWidget(self.label, 0, 0, 1, 1)
        self.lineEdit = QtGui.QLineEdit(Form)
        self.lineEdit.setObjectName(_fromUtf8("lineEdit"))
        self.gridLayout.addWidget(self.lineEdit, 0, 1, 1, 1)
        self.lineEdit_2 = QtGui.QLineEdit(Form)
        self.lineEdit_2.setObjectName(_fromUtf8("lineEdit_2"))
        self.gridLayout.addWidget(self.lineEdit_2, 1, 1, 1, 1)
        self.pushButton_2 = QtGui.QPushButton(Form)
        self.pushButton_2.setStyleSheet(_fromUtf8("color: rgb(255, 255, 255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.pushButton_2.setObjectName(_fromUtf8("pushButton_2"))
        self.pushButton_2.clicked.connect(self.Back)
        self.gridLayout.addWidget(self.pushButton_2, 2, 0, 1, 1)
        self.pushButton = QtGui.QPushButton(Form)
        self.pushButton.setStyleSheet(_fromUtf8("color: rgb(255, 255, 255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.gridLayout.addWidget(self.pushButton, 2, 1, 1, 1)
        self.label_2 = QtGui.QLabel(Form)
        self.label_2.setStyleSheet(_fromUtf8("color: rgb(255, 255, 255);\n"
"font: 63 oblique 12pt \"URW Gothic L\";"))
        self.label_2.setObjectName(_fromUtf8("label_2"))
        self.gridLayout.addWidget(self.label_2, 1, 0, 1, 1)

        self.retranslateUi(Form)
        QtCore.QMetaObject.connectSlotsByName(Form)

    def retranslateUi(self, Form):
        Form.setWindowTitle(_translate("Form", "Form", None))
        self.label.setText(_translate("Form", "Enter User Name", None))
        self.pushButton_2.setText(_translate("Form", "Cancel", None))
        self.pushButton.setText(_translate("Form", "OK", None))
        self.label_2.setText(_translate("Form", "Enter Password", None))

import iamge_rc

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    Form = QtGui.QWidget()
    ui = Ui_Form()
    ui.setupUi(Form)
    Form.show()
    sys.exit(app.exec_())

import SignIn -> code of SignIN

import WelFrame-> code of Welcome Window

Answer 1

I continually recommend that you do not modify the files that Qt Designer creates. These classes are oriented to the design so the most elegant thing is to create a class that implements the logic and use the previous design, the classes must have the following structure:

class LogicClass(QWidget, Ui_SomeDesign):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setupUi(self)

So I recommend you remove all the modifications to your design classes or create them using pyuic.

In your case I recommend creating another file called main.py that is in the same folder as your other scripts:

.
├── main.py <-- new file
├── SignIn.py
└── WelFrame.py

In this file we create the classes that implement the logic for your designs and implement a method that performs the task of closing the current widget and displaying the new widget

import sys
from PyQt4.QtGui import QWidget, QApplication

from SignIn import Ui_Form as SignInForm
from WelFrame import Ui_Form as WelFrameForm


class Sign(QWidget, SignInForm):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setupUi(self)


class WelFrame(QWidget, WelFrameForm):
    def __init__(self, parent=None):
        QWidget.__init__(self, parent)
        self.setupUi(self)

def foo(w1, w2):
    w1.show()
    w2.hide()

if __name__ == '__main__':
    app = QApplication(sys.argv)
    wel = WelFrame()
    sign = Sign()
    wel.pushButton_2.clicked.connect(lambda : foo(sign, wel))
    sign.pushButton_2.clicked.connect(lambda: foo(wel, sign))
    wel.show()
    sys.exit(app.exec_())