Python QtGui: inheritance of variables between classes

Question

I'm very new to GUIs and I have a quick question on inheritance of variables.

In my GUI i have two buttons, one selects an xlsx file, the other graphs it. The first class below sets the buttons and selects the file:

class Example(QtGui.QWidget):

def __init__(self):
    super(Example, self).__init__()

    self.initUI()

def initUI(self):

    vBoxLayout = QtGui.QVBoxLayout(self)

    file_btn = QtGui.QPushButton('Select File', self)
    file_btn.clicked.connect(self.get_graph_file)

    graphing_btn = QtGui.QPushButton('Plot Graph', self)
    graphing_btn.clicked.connect(Plotting_Graph)

    self.show()

def get_graph_file(self):

    fname_graphfile = QtGui.QFileDialog.getOpenFileName(self, 'Open file', '/Users/.../', 'excel files (*.xlsx)')

... and the second should inherit fname_graphfile and graph it (I've only added in a bit of the graphing code)...

class Plotting_Graph(Example):

def __init__(self):

    self.PlottingGraph()

def PlottingGraph(self):

    xl = ef(fname_graphfile[0])......

When run, it gives an error global name 'fname_graphfile' is not defined.

How do I get the second class to remember something I've defined in the previous class?

Answer 1

fname_graphfile is a local variable in the get_graph_file so other methods don't have access to it what you should do is make it an instance attribute so it can be accessed from any method and then add an argument to Plotting_Graph.PlottingGraph that accepts the xlsx file as a parameter to the method and pass self.fname_graphfile to it from the button click

your final code should look like this

from PyQt4 import QtCore, QtGui
import sys

class Example(QtGui.QWidget):

    def __init__(self):
        super(Example, self).__init__()
        self.initUI()

    def initUI(self):
        self.fname_graph_file = ''
        file_btn = QtGui.QPushButton('Select File', self)
        file_btn.setGeometry(100, 100, 150, 30)
        file_btn.clicked.connect(self.get_graph_file)

        graphing_btn = QtGui.QPushButton('Plot Graph', self)

        plot = Plotting_Graph()
        graphing_btn.clicked.connect(lambda: plot.PlottingGraph(self.fname_graph_file))

        self.show()

    def get_graph_file(self):

        self.fname_graph_file = QtGui.QFileDialog.getOpenFileName(self, 'Open file', '/home', 'excel files (*.xlsx)')

class Plotting_Graph(Example):

    def __init__(self):
        pass

    def PlottingGraph(self, fname_graphfile):

        print(fname_graphfile)
        # xl = ef(fname_graphfile[0])

app =  QtGui.QApplication([])
a = Example()
app.exec_()