How to determine an active screen (monitor) of my Application (window) using python PyQt5?

One solution I came across is to use a temporary QApplication():

import sys
from PyQt5 import QtWidgets, QtCore, QtGui

# fire up a temporary QApplication
def get_resolution():

    app = QtWidgets.QApplication(sys.argv)

    print(app.primaryScreen())

    d = app.desktop()

    print(d.screenGeometry())
    print(d.availableGeometry())
    print(d.screenCount())    

    g = d.screenGeometry()
    return (g.width(), g.height())

x, y = get_resolution()

if x > 1920 and y > 1080:
  QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling, True)
  QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps, True)
else:
  QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling, False)
  QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps, False)

# Now your code ...

This function will detect all attached screens:

# fire up a temporary QApplication
def get_resolution_multiple_screens():

    app = QtGui.QGuiApplication(sys.argv)
    #QtWidgets.QtGui
    all_screens = app.screens()

    for s in all_screens:

        print()
        print(s.name())
        print(s.availableGeometry())
        print(s.availableGeometry().width())
        print(s.availableGeometry().height())
        print(s.size())
        print(s.size().width())
        print(s.size().height())

    print()
    print('primary:', app.primaryScreen())
    print('primary:', app.primaryScreen().availableGeometry().width())
    print('primary:', app.primaryScreen().availableGeometry().height())

    # now choose one

You can use the hints here and here to get the screen where the application is running.

But I think primaryScreen should also return this:

primaryScreen : QScreen* const

This property holds the primary (or default) screen of the application.

This will be the screen where QWindows are initially shown, unless otherwise specified.

(https://doc.qt.io/qt-5/qguiapplication.html#primaryScreen-prop)

Well, after creating the MainWindow, you can just call QMainWindow.screen(). This returns the current screen the MainWindow is on. This would at least allow you to check the screen resolution at the start of your application. Right now there is no such thing as a screenChangeEvent. However i am sure you can create one by subclassing the MainWindow and overloading the QMainWindow.moveEvent

For example:

    class MainWindow(QtWidgets.QMainWindow):
        screenChanged = QtCore.pyqtSignal(QtGui.QScreen, QtGui.QScreen)

        def moveEvent(self, event):
            oldScreen = QtWidgets.QApplication.screenAt(event.oldPos())
            newScreen = QtWidgets.QApplication.screenAt(event.pos())

            if not oldScreen == newScreen:
                self.screenChanged.emit(oldScreen, newScreen)

            return super().moveEvent(event)

This checks if the screen has changed. If it has it emits a signal. Now you only need to connect this signal to a function that sets your dpi attributes. The event gives you access to the old and to the new screen.

Warning:

One of the screen can be None at the start of your application because there is no oldScreen when you first start your application. So please check this.

Though i could not get the direct solution I am able to develop a method to get what I was looking. With the help of few links and previous post I am able to achieve. with this post I got an idea of tracking the mouse event.

I developed a method to track all the monitors and respective staring positions. if my variable naming is not appropriate I am happy to accept the changes

def get_screen_resolution():
  app = QApplication(sys.argv)
  screen_count = QGuiApplication.screens()
  resolutions_in_x = []

  for index, screen_names in enumerate(screen_count):
    resolution = screen_count[index].size()
    height = resolution.height()
    width = resolution.width()
    resolutions_in_x.append(width)

  low_resolution_monitors = {}
  high_resolution_monitors = {}

  for i, wid_res in enumerate(resolutions_in_x):
    if wid_res > 1920:
      high_resolution_monitors.update({i: wid_res})
    else:
      low_resolution_monitors.update({'L': wid_res})    
  temp_value = 0
  high_res_monitors_x_position = []
  low_res_monitors_x_position = []
  for i in range(len(screen_count)):
    temp_value = temp_value+resolutions_in_x[i]
      if resolutions_in_x[i] in high_resolution_monitors.values():
        high_res_monitors_x_position.append(temp_value-resolutions_in_x[i])
      else:
        low_res_monitors_x_position.append(temp_value-resolutions_in_x[i])

  total_width_res = []
  pixel_value = 0
  first_pixel = 0
  for i, wid_value in enumerate(resolutions_in_x):
    pixel_value = pixel_value + wid_value
    total_width_res.append(tuple((first_pixel, pixel_value-1)))
    first_pixel = pixel_value

  return high_res_monitors_x_position, low_res_monitors_x_position, total_width_res


def moveEvent(self, event):

screen_pos = self.pos()
screen_dimensions = [screen_pos.x(),screen_pos.y()]
super(MainWindow, self).moveEvent(event)

Window_starting_pt = screen_pos.x()
for i, value in enumerate(self.total_width_res):
  if value[0]<=Window_starting_pt+30 <=value[1] or value[0]<=Window_starting_pt-30 <=value[1]: #taking 30pixels as tolerance since widgets are staring at some negative pixel values
    if value[0] in self.high_res_monitors_x_position:
      QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling, True)
      QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps, True)
    else:
      QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling, False)
      QtWidgets.QApplication.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps, False)

With aboe two functions am able to track my application(window) position and also able to track when ever it is dragged among windows