Example in PyQT5

TestPyQt5_.idea_inspectionProfiles_profiles_settings.xml

<component name="InspectionProjectProfileManager">
  <settings>
    <option name="USE_PROJECT_PROFILE" value="false" />
    <version value="1.0" />
  </settings>
</component>

TestPyQt5_.idea_misc.xml

<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
  <component name="ProjectRootManager" version="2" project-jdk-name="Python 3.8" project-jdk-type="Python SDK" />
</project>

TestPyQt5_.idea_modules.xml

<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
  <component name="ProjectModuleManager">
    <modules>
      <module fileurl="file://$PROJECT_DIR$/.idea/TestPyQt5.iml" filepath="$PROJECT_DIR$/.idea/TestPyQt5.iml" />
    </modules>
  </component>
</project>

TestPyQt5_.idea_TestPyQt5.iml

<?xml version="1.0" encoding="UTF-8"?>
<module type="PYTHON_MODULE" version="4">
  <component name="NewModuleRootManager">
    <content url="file://$MODULE_DIR$" />
    <orderEntry type="inheritedJdk" />
    <orderEntry type="sourceFolder" forTests="false" />
  </component>
</module>

TestPyQt5_.idea_workspace.xml

<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
  <component name="ChangeListManager">
    <list default="true" id="442970e4-31b9-426a-be4a-b8c3f6d7367d" name="Default Changelist" comment="" />
    <option name="SHOW_DIALOG" value="false" />
    <option name="HIGHLIGHT_CONFLICTS" value="true" />
    <option name="HIGHLIGHT_NON_ACTIVE_CHANGELIST" value="false" />
    <option name="LAST_RESOLUTION" value="IGNORE" />
  </component>
  <component name="FileTemplateManagerImpl">
    <option name="RECENT_TEMPLATES">
      <list>
        <option value="Python Script" />
      </list>
    </option>
  </component>
  <component name="ProjectId" id="1e6yR92Sxo3SUw8MSg1RnVrB09i" />
  <component name="ProjectViewState">
    <option name="hideEmptyMiddlePackages" value="true" />
    <option name="showExcludedFiles" value="true" />
    <option name="showLibraryContents" value="true" />
  </component>
  <component name="PropertiesComponent">
    <property name="RunOnceActivity.ShowReadmeOnStart" value="true" />
    <property name="last_opened_file_path" value="$PROJECT_DIR$" />
  </component>
  <component name="RecentsManager">
    <key name="CopyFile.RECENT_KEYS">
      <recent name="C:\Users\lrmendiburo\PycharmProjects\TestPyQt5" />
    </key>
  </component>
  <component name="RunManager" selected="Python.aplicacionPrincipal">
    <configuration name="aplicacionPrincipal (1)" type="PythonConfigurationType" factoryName="Python" temporary="true" nameIsGenerated="true">
      <module name="TestPyQt5" />
      <option name="INTERPRETER_OPTIONS" value="" />
      <option name="PARENT_ENVS" value="true" />
      <envs>
        <env name="PYTHONUNBUFFERED" value="1" />
      </envs>
      <option name="SDK_HOME" value="" />
      <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
      <option name="IS_MODULE_SDK" value="true" />
      <option name="ADD_CONTENT_ROOTS" value="true" />
      <option name="ADD_SOURCE_ROOTS" value="true" />
      <option name="SCRIPT_NAME" value="$PROJECT_DIR$/aplicacionPrincipal.py" />
      <option name="PARAMETERS" value="" />
      <option name="SHOW_COMMAND_LINE" value="false" />
      <option name="EMULATE_TERMINAL" value="false" />
      <option name="MODULE_MODE" value="false" />
      <option name="REDIRECT_INPUT" value="false" />
      <option name="INPUT_FILE" value="" />
      <method v="2" />
    </configuration>
    <configuration name="aplicacionPrincipal" type="PythonConfigurationType" factoryName="Python" temporary="true" nameIsGenerated="true">
      <module name="TestPyQt5" />
      <option name="INTERPRETER_OPTIONS" value="" />
      <option name="PARENT_ENVS" value="true" />
      <envs>
        <env name="PYTHONUNBUFFERED" value="1" />
      </envs>
      <option name="SDK_HOME" value="" />
      <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
      <option name="IS_MODULE_SDK" value="true" />
      <option name="ADD_CONTENT_ROOTS" value="true" />
      <option name="ADD_SOURCE_ROOTS" value="true" />
      <option name="SCRIPT_NAME" value="C:\Users\lrmendiburo\PycharmProjects\TestPyQt5\aplicacionPrincipal.py" />
      <option name="PARAMETERS" value="" />
      <option name="SHOW_COMMAND_LINE" value="false" />
      <option name="EMULATE_TERMINAL" value="false" />
      <option name="MODULE_MODE" value="false" />
      <option name="REDIRECT_INPUT" value="false" />
      <option name="INPUT_FILE" value="" />
      <method v="2" />
    </configuration>
    <configuration name="aplicacionVentana1" type="PythonConfigurationType" factoryName="Python" temporary="true" nameIsGenerated="true">
      <module name="TestPyQt5" />
      <option name="INTERPRETER_OPTIONS" value="" />
      <option name="PARENT_ENVS" value="true" />
      <envs>
        <env name="PYTHONUNBUFFERED" value="1" />
      </envs>
      <option name="SDK_HOME" value="" />
      <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
      <option name="IS_MODULE_SDK" value="true" />
      <option name="ADD_CONTENT_ROOTS" value="true" />
      <option name="ADD_SOURCE_ROOTS" value="true" />
      <option name="SCRIPT_NAME" value="$PROJECT_DIR$/aplicacionVentana1.py" />
      <option name="PARAMETERS" value="" />
      <option name="SHOW_COMMAND_LINE" value="false" />
      <option name="EMULATE_TERMINAL" value="false" />
      <option name="MODULE_MODE" value="false" />
      <option name="REDIRECT_INPUT" value="false" />
      <option name="INPUT_FILE" value="" />
      <method v="2" />
    </configuration>
    <configuration name="aplicacionVentana2" type="PythonConfigurationType" factoryName="Python" temporary="true" nameIsGenerated="true">
      <module name="TestPyQt5" />
      <option name="INTERPRETER_OPTIONS" value="" />
      <option name="PARENT_ENVS" value="true" />
      <envs>
        <env name="PYTHONUNBUFFERED" value="1" />
      </envs>
      <option name="SDK_HOME" value="" />
      <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
      <option name="IS_MODULE_SDK" value="true" />
      <option name="ADD_CONTENT_ROOTS" value="true" />
      <option name="ADD_SOURCE_ROOTS" value="true" />
      <option name="SCRIPT_NAME" value="$PROJECT_DIR$/aplicacionVentana2.py" />
      <option name="PARAMETERS" value="" />
      <option name="SHOW_COMMAND_LINE" value="false" />
      <option name="EMULATE_TERMINAL" value="false" />
      <option name="MODULE_MODE" value="false" />
      <option name="REDIRECT_INPUT" value="false" />
      <option name="INPUT_FILE" value="" />
      <method v="2" />
    </configuration>
    <configuration name="test" type="PythonConfigurationType" factoryName="Python" temporary="true" nameIsGenerated="true">
      <module name="TestPyQt5" />
      <option name="INTERPRETER_OPTIONS" value="" />
      <option name="PARENT_ENVS" value="true" />
      <envs>
        <env name="PYTHONUNBUFFERED" value="1" />
      </envs>
      <option name="SDK_HOME" value="" />
      <option name="WORKING_DIRECTORY" value="$PROJECT_DIR$" />
      <option name="IS_MODULE_SDK" value="true" />
      <option name="ADD_CONTENT_ROOTS" value="true" />
      <option name="ADD_SOURCE_ROOTS" value="true" />
      <option name="SCRIPT_NAME" value="$PROJECT_DIR$/test.py" />
      <option name="PARAMETERS" value="" />
      <option name="SHOW_COMMAND_LINE" value="false" />
      <option name="EMULATE_TERMINAL" value="false" />
      <option name="MODULE_MODE" value="false" />
      <option name="REDIRECT_INPUT" value="false" />
      <option name="INPUT_FILE" value="" />
      <method v="2" />
    </configuration>
    <recent_temporary>
      <list>
        <item itemvalue="Python.aplicacionPrincipal" />
        <item itemvalue="Python.test" />
        <item itemvalue="Python.aplicacionPrincipal (1)" />
        <item itemvalue="Python.aplicacionVentana2" />
        <item itemvalue="Python.aplicacionVentana1" />
      </list>
    </recent_temporary>
  </component>
  <component name="SvnConfiguration">
    <configuration />
  </component>
  <component name="TaskManager">
    <task active="true" id="Default" summary="Default task">
      <changelist id="442970e4-31b9-426a-be4a-b8c3f6d7367d" name="Default Changelist" comment="" />
      <created>1593656325616</created>
      <option name="number" value="Default" />
      <option name="presentableId" value="Default" />
      <updated>1593656325616</updated>
    </task>
    <servers />
  </component>
  <component name="WindowStateProjectService">
    <state x="413" y="115" key="#com.intellij.refactoring.safeDelete.UnsafeUsagesDialog" timestamp="1593704734734">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state x="413" y="115" key="#com.intellij.refactoring.safeDelete.UnsafeUsagesDialog/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593704734734" />
    <state x="438" y="71" key="#xdebugger.evaluate" timestamp="1593705459194">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state x="438" y="71" key="#xdebugger.evaluate/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705459194" />
    <state x="463" y="123" key="FileChooserDialogImpl" timestamp="1593659423589">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state x="463" y="123" key="FileChooserDialogImpl/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593659423589" />
    <state width="1345" height="227" key="GridCell.Tab.0.bottom" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.0.bottom/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.0.center" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.0.center/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.0.left" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.0.left/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.0.right" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.0.right/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.1.bottom" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.1.bottom/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.1.center" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.1.center/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.1.left" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.1.left/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
    <state width="1345" height="227" key="GridCell.Tab.1.right" timestamp="1593705727419">
      <screen x="0" y="0" width="1366" height="738" />
    </state>
    <state width="1345" height="227" key="GridCell.Tab.1.right/0.0.1366.738/-1366.0.1366.738@0.0.1366.738" timestamp="1593705727419" />
  </component>
</project>

TestPyQt5_aplicacionPrincipal.py

import sys
from PyQt5.QtWidgets import QDialog, QApplication
from main import *
import aplicacionVentana1
import aplicacionVentana2


class aplicacionPrincipal(QDialog):
    def __init__(self):
        super().__init__()
        self.ventanaPrincipal = Ui_DialogMain()
        self.ventanaPrincipal.setupUi(self)

        self.ventanaPrincipal.btn_Ventana1.clicked.connect(self.mostrarVentana1)
        self.ventanaPrincipal.btn_Ventana2.clicked.connect(self.mostrarVentana2)
        self.ventanaPrincipal.pushButton.clicked.connect(self.cerrar)
        self.show()

    def mostrarVentana1(self):
        print("Abrir Ventana1")
        aplicacionVentana1.ventana1.show()

    def mostrarVentana2(self):
        print("Abrir Ventana2")
        aplicacionVentana2.ventana2.show()

    def cerrar(self):
        print("Cerrar Ventana")
        sys.exit()


if __name__ == '__main__':
    app = QApplication(sys.argv)
    ventanaPrincipal = aplicacionPrincipal()
    ventanaPrincipal.show()
    sys.exit(app.exec_())

TestPyQt5_aplicacionVentana1.py

import sys
from PyQt5.QtWidgets import QDialog, QApplication
from ventana1 import *


class aplicacionVentana1(QDialog):
    def __init__(self):
        super().__init__()
        self.ventana1 = Ui_DialogVentana1()
        self.ventana1.setupUi(self)

        self.ventana1.pushButton.clicked.connect(self.volver)

    def volver(self):
        print("Volviendo desde la ventana 1")
        self.close()

app = QApplication(sys.argv)
ventana1 = aplicacionVentana1()

TestPyQt5_aplicacionVentana2.py

import sys
from PyQt5.QtWidgets import QDialog, QApplication
from ventana2 import *


class aplicacionVentana2(QDialog):
    def __init__(self):
        super().__init__()
        self.ventana2 = Ui_DialogVentana2()
        self.ventana2.setupUi(self)

        self.ventana2.pushButton.clicked.connect(self.volver)

    def volver(self):
        print("Volviendo desde la ventana 2")
        self.close()

app = QApplication(sys.argv)
ventana2 = aplicacionVentana2()

TestPyQt5_main.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'main.ui'
#
# Created by: PyQt5 UI code generator 5.15.0
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_DialogMain(object):
    def setupUi(self, DialogMain):
        DialogMain.setObjectName("DialogMain")
        DialogMain.resize(180, 161)
        self.lbl_Saludo = QtWidgets.QLabel(DialogMain)
        self.lbl_Saludo.setGeometry(QtCore.QRect(10, 10, 111, 21))
        self.lbl_Saludo.setObjectName("lbl_Saludo")
        self.btn_Ventana1 = QtWidgets.QPushButton(DialogMain)
        self.btn_Ventana1.setGeometry(QtCore.QRect(50, 40, 75, 23))
        self.btn_Ventana1.setObjectName("btn_Ventana1")
        self.btn_Ventana2 = QtWidgets.QPushButton(DialogMain)
        self.btn_Ventana2.setGeometry(QtCore.QRect(50, 80, 75, 23))
        self.btn_Ventana2.setObjectName("btn_Ventana2")
        self.pushButton = QtWidgets.QPushButton(DialogMain)
        self.pushButton.setGeometry(QtCore.QRect(50, 120, 75, 23))
        self.pushButton.setObjectName("pushButton")

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

    def retranslateUi(self, DialogMain):
        _translate = QtCore.QCoreApplication.translate
        DialogMain.setWindowTitle(_translate("DialogMain", "Main"))
        self.lbl_Saludo.setText(_translate("DialogMain", "Selecciona la ventana:"))
        self.btn_Ventana1.setText(_translate("DialogMain", "Ventana1"))
        self.btn_Ventana2.setText(_translate("DialogMain", "Ventana2"))
        self.pushButton.setText(_translate("DialogMain", "Cerrar"))

TestPyQt5_main.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>DialogMain</class>
 <widget class="QDialog" name="DialogMain">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>180</width>
    <height>161</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Main</string>
  </property>
  <widget class="QLabel" name="lbl_Saludo">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>10</y>
     <width>111</width>
     <height>21</height>
    </rect>
   </property>
   <property name="text">
    <string>Selecciona la ventana:</string>
   </property>
  </widget>
  <widget class="QPushButton" name="btn_Ventana1">
   <property name="geometry">
    <rect>
     <x>50</x>
     <y>40</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>Ventana1</string>
   </property>
  </widget>
  <widget class="QPushButton" name="btn_Ventana2">
   <property name="geometry">
    <rect>
     <x>50</x>
     <y>80</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>Ventana2</string>
   </property>
  </widget>
  <widget class="QPushButton" name="pushButton">
   <property name="geometry">
    <rect>
     <x>50</x>
     <y>120</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>Cerrar</string>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>

TestPyQt5_ventana1.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'ventana1.ui'
#
# Created by: PyQt5 UI code generator 5.15.0
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_DialogVentana1(object):
    def setupUi(self, DialogVentana1):
        DialogVentana1.setObjectName("DialogVentana1")
        DialogVentana1.resize(320, 84)
        self.label = QtWidgets.QLabel(DialogVentana1)
        self.label.setGeometry(QtCore.QRect(10, 10, 141, 16))
        self.label.setObjectName("label")
        self.pushButton = QtWidgets.QPushButton(DialogVentana1)
        self.pushButton.setGeometry(QtCore.QRect(120, 40, 75, 23))
        self.pushButton.setObjectName("pushButton")

        self.retranslateUi(DialogVentana1)
        QtCore.QMetaObject.connectSlotsByName(DialogVentana1)

    def retranslateUi(self, DialogVentana1):
        _translate = QtCore.QCoreApplication.translate
        DialogVentana1.setWindowTitle(_translate("DialogVentana1", "Ventana1"))
        self.label.setText(_translate("DialogVentana1", "Esta es la ventana numero 1:"))
        self.pushButton.setText(_translate("DialogVentana1", "<< Volver"))

TestPyQt5_ventana1.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>DialogVentana1</class>
 <widget class="QDialog" name="DialogVentana1">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>320</width>
    <height>84</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Ventana1</string>
  </property>
  <widget class="QLabel" name="label">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>10</y>
     <width>141</width>
     <height>16</height>
    </rect>
   </property>
   <property name="text">
    <string>Esta es la ventana numero 1:</string>
   </property>
  </widget>
  <widget class="QPushButton" name="pushButton">
   <property name="geometry">
    <rect>
     <x>120</x>
     <y>40</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>&lt;&lt; Volver</string>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>

TestPyQt5_ventana2.py

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'ventana2.ui'
#
# Created by: PyQt5 UI code generator 5.15.0
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_DialogVentana2(object):
    def setupUi(self, DialogVentana2):
        DialogVentana2.setObjectName("DialogVentana2")
        DialogVentana2.resize(320, 88)
        self.label = QtWidgets.QLabel(DialogVentana2)
        self.label.setGeometry(QtCore.QRect(10, 10, 151, 16))
        self.label.setObjectName("label")
        self.pushButton = QtWidgets.QPushButton(DialogVentana2)
        self.pushButton.setGeometry(QtCore.QRect(120, 40, 75, 23))
        self.pushButton.setObjectName("pushButton")

        self.retranslateUi(DialogVentana2)
        QtCore.QMetaObject.connectSlotsByName(DialogVentana2)

    def retranslateUi(self, DialogVentana2):
        _translate = QtCore.QCoreApplication.translate
        DialogVentana2.setWindowTitle(_translate("DialogVentana2", "Ventana2"))
        self.label.setText(_translate("DialogVentana2", "Esta es la ventana numero 2:"))
        self.pushButton.setText(_translate("DialogVentana2", "<< Volver"))

TestPyQt5_ventana2.ui

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>DialogVentana2</class>
 <widget class="QDialog" name="DialogVentana2">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>320</width>
    <height>88</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Ventana2</string>
  </property>
  <widget class="QLabel" name="label">
   <property name="geometry">
    <rect>
     <x>10</x>
     <y>10</y>
     <width>151</width>
     <height>16</height>
    </rect>
   </property>
   <property name="text">
    <string>Esta es la ventana numero 2:</string>
   </property>
  </widget>
  <widget class="QPushButton" name="pushButton">
   <property name="geometry">
    <rect>
     <x>120</x>
     <y>40</y>
     <width>75</width>
     <height>23</height>
    </rect>
   </property>
   <property name="text">
    <string>&lt;&lt; Volver</string>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections/>
</ui>