PyQT5 TypeError: startfile: filepath should be string, bytes or os.PathLike, not Ui_MainWindow

Question

I'm trying to build an app here. I used QT Designer to build the main window (Ui_MainWindow) with buttons. I import this to a new file where I can structure the code a bit better.

Anyhow, I keep getting the error "TypeError: startfile: filepath should be string, bytes or os.PathLike, not Ui_MainWindow" whenever I try to get the filename via QFileDialog. This filename is used in the GetData -method to produce a dataframe. I'm sure I'm doing something horribly wrong here in my code. I understood that you can call methods within other methods

So I will have 3 buttons:

1. Open folder (which gets the filename)
2. Update data (which is connected to UpdateData method. This method updates the data as I want)
3. Calculate (a method that calculates something based on the output from updateData -method.)

So I am trying to get an output from step 1 to use as input in step 2, to get an output which then would be used as input in step 3 and then - voilá.

What am I doing wrong?

from myQTDesignerGUIfile import Ui_MainWindow
from PyQt5 import QtWidgets
from PyQt5.QtWidgets import (QApplication, QMainWindow, QPushButton, QLabel, QFileDialog, QMessageBox)
from PyQt5.QtCore import pyqtSlot, QFileInfo
 
class MyApp(QtWidgets.QMainWindow, Ui_MainWindow):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        
        #Build instance of setpUI in Ui_MainWindow -class
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        
    def GetFileName(self):
        FileFilter = 'File (*.xlsx *.xlsm *.csv)'
        FileName = QFileDialog.getOpenFileName(parent = self,
                                                caption="Select File",
                                                directory = 'Some Path',
                                                filter = FileFilter)[0]
        
        path = str(FileName)
        if path:
           print(path)
           return path

    def GetData(self):
        path = self.GetFileName
        return pd.read_csv(path)
    
    def UpdateData(self):
        ## get data using the GetData -method
        df = self.GetData()
        
        ## code to modify data is written here
        
        return final_mod_data

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    w = MyApp()
    w.show()
    app.exec()