使用 Pandas df 存储用户输入，同时使用 Kivy 和 Python

Question

I do need to store User input in a Pandas Dataframe. While launching the Programm the df should be empty. on every screen there will be a new df generated and should be added ( concat for example ) to the main df. So i need to make the df and all changes availabe as a local variable in any screen.

maindf= pd.DataFrame()

now on the next screen:

class screen1(Screen):
    def redo(self):
        pass
    def press(self):
        
        maindf['col'] = pd.Series([ 'A'for x in range(len(Folgenzähler))])
        pass

on the next screen i want to do the following:

 class screen2(Screen):
    def press(self):
        values = []
        row = self.ids.Peter
        for row in row.children:
            for ch in reversed(row.children):
                if isinstance(ch, TextInput):
                    a = ch.text
                    print("Row 1 ist"+str(a))
                    values.append(str(a))
        
        hilf2 = copy.deepcopy(values)
        hilf2 = ' '.join(hilf2).split()
        hilf2 = np.array(hilf2).reshape(len(Folgenzähler), 3)

        datatoappend= pd.DataFrame(hilf2, columns=['A', 'B', 'C'])
        maindf= pd.concat([maindf, datatoappend], axis=1)

        print("Pandas maindf")
        print(maindf)

Afterwards the printed DF (maindf )should contain the columns ['col','A','B','C'] and their user generated Input Values. So i need to know how to set up a DF which is available for all screens. I could store the main df as a csv and make any screen read this csv file. But this does feel pretty bad. right now i just get:

     maindf= pd.concat([maindf, datatoappend], axis=1)

UnboundLocalError: local variable 'maindf' referenced before assignment

Answer 1

I found a nice approach using global as a workaround. I just had to add some extra code i did change on the first screen:

class screen1(Screen):
    def redo(self):
        pass
    def press(self):
        global maindf
        maindf = pd.DataFrame()
        maindf['col'] = pd.Series([ 'A'for x in range(len(Folgenzähler))])
        pass

and on the second screen i did add global again.

class screen2(Screen):
    def press(self):
        values = []
        row = self.ids.Peter
        for row in row.children:
            for ch in reversed(row.children):
                if isinstance(ch, TextInput):
                    a = ch.text
                    print("Row 1 ist"+str(a))
                    values.append(str(a))
        
        hilf2 = copy.deepcopy(values)
        hilf2 = ' '.join(hilf2).split()
        hilf2 = np.array(hilf2).reshape(len(Folgenzähler), 3)

        datatoappend= pd.DataFrame(hilf2, columns=['A', 'B', 'C'])
        global maindf
        maindf= pd.concat([maindf, datatoappend], axis=1)

        print("Pandas maindf")
        print(maindf)

Maybe there are some better ways to do this. Feel free to contribute alternative approaches, critics or additional Information.