change label from other class in a different file

Question

I am creating an application where I have a main window whit a label and then a docked widget that is in another file. I want to change the main windows label from a button

Answer 1

You are using the wrong tools, for example your code has a circular import that causes your application to close since it is equivalent to a while True.

In Qt, signals and slots are used to share data asynchronously, as well as contributing to the fact that there is no coupling between classes. In your case, Results_Window must have a signal that transmits that information to the MainWindow, this signal must be emit within clickMethod.

results_window.py

from PyQt5 import QtCore, QtWidgets

class Results_Window(QtWidgets.QWidget):
    resultChanged = QtCore.pyqtSignal(str)

    def __init__(self):
        super(Results_Window, self).__init__()
        print("init")

        self.label = QtWidgets.QLabel()
        self.value = QtWidgets.QLineEdit()

        self.bt = QtWidgets.QPushButton("Click")
        self.bt.clicked.connect(self.clickMethod)

        main_layout = QtWidgets.QVBoxLayout(self)
        main_layout.addWidget(self.label)
        main_layout.addWidget(self.value)
        main_layout.addWidget(self.bt)

    @QtCore.pyqtSlot()
    def clickMethod(self):
        text = self.value.text()
        self.resultChanged.emit(text)

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    app.setStyle('Fusion')
    w = Results_Window()
    w.show()
    sys.exit(app.exec_())

main_window.py

from PyQt5 import QtCore, QtGui, QtWidgets
import results_window

class MainWindow(QtWidgets.QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.define_main_windows()
        self.create_dock_widgets()

    def define_main_windows(self):
        self.setMinimumSize(QtCore.QSize(300, 100))    
        self.setWindowTitle("Python SkyLibris") 
        self.setWindowIcon(QtGui.QIcon("skylibris_icon.png"))
        self.setStyleSheet("QMainWindow {background: 'white';}")
        top, left, width, height = 50, 0, 1300, 400
        self.setGeometry(left, top, width, height)
        self.result = QtWidgets.QLabel("result:")
        self.setCentralWidget(self.result)

    def create_dock_widgets(self):
        self.results_window = results_window.Results_Window()
        self.results_window.resultChanged.connect(self.result.setText)
        self.resultsWindowDock = QtWidgets.QDockWidget("Results Viewer", self)
        self.resultsWindowDock.setWidget(self.results_window )
        self.resultsWindowDock.setFloating(False)
        self.resultsWindowDock.setVisible(True)
        self.addDockWidget(QtCore.Qt.LeftDockWidgetArea, self.resultsWindowDock)

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    app.setStyle('Fusion')
    mainWin = MainWindow()
    mainWin.show()
    sys.exit(app.exec_())