Q:

How to access a text file stored under a variable name

When trying to access an external text file from Python, I am encountering a couple of issues when trying to simply view the contents of the file and when trying to add to the file. The part of the program involved takes a username and creates a text file under this username if it does not already exist. When using the Create() function, I encounter the following TypeError:
Exception in Tkinter callback
Traceback (most recent call last):
  File "D:\Python 3.3.2\A Level Computer Science\stackoverflowsolution.py", line 48, in View
    with open(userfile, 'r') as u:
FileNotFoundError: [Errno 2] No such file or directory: 'name.txt'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "D:\Python 3.3.2\Python files\lib\tkinter\__init__.py", line 1475, in __call__
    return self.func(*args)
  File "D:\Python 3.3.2\A Level Computer Science\stackoverflowsolution.py", line 91, in Add
    u.write(addText.get())
TypeError: get() missing 1 required positional argument: 'index1'

This is the code that encounters the errors:
from tkinter import *
import os

def Login():

    global nameEL
    global rootA

    rootA = Tk()
    rootA.title('Login')

    intruction = Label(rootA, text='Please Login\n')
    intruction.grid(sticky=E)

    nameL = Label(rootA, text='Username: ')
    nameL.grid(row=1, sticky=W)

    nameEL = Entry(rootA)
    nameEL.grid(row=1, column=1)

    loginB = Button(rootA, text='Login', command=LoggedIn)
    loginB.grid(columnspan=2, sticky=W)
    rootA.mainloop()

def LoggedIn():

    global userfile

    roots1 = Tk()
    roots1.title('Logged in successfully')
    roots1.geometry('300x300')

    userfile = nameEL.get() + '.txt'

    View1 = Button(roots1, text='View', command=View)
    View1.grid(columnspan=10, sticky=W)
    View1.pack(fill = 'x')

    Create1 = Button(roots1, text='Create', command=Create)
    Create1.grid(columnspan=10, sticky=W)
    Create1.pack(fill = 'x')

def View():

    global userfile

    try:
        with open(userfile, 'r') as u:
            print(u.read())
    except FileNotFoundError:
        r = Tk()
        r.title('View')
        r.geometry('300x50')
        rlbl = Label(r, text='\n[!] Theres nothing to see here [!]')
        rlbl.pack()
        r.mainloop()
        LoggedIn()
    except ValueError:
        r = Tk()
        r.title('View')
        r.geometry('300x50')
        rlbl.pack()
        r.mainloop()
        LoggedIn()

def Create():

    global addText
    global rootC

    rootC = Tk()
    rootC.title('Lets add some information')
    instruction = Label(rootC, text='Please enter the information you would like to add\n')
    instruction.grid(row=0, column=0, sticky=W)

    newText = Label(rootC, text='info: ')
    newText.grid(row=1, column=0)

    addText = Text(rootC)
    addText.grid(row=2, column=0)

    addButton = Button(rootC, text='Add', command=Add)
    addButton.grid(columnspan=2, sticky=W)
    addButton.grid(row=3, column=0)

def Add():

    global userfile

    with open(userfile, 'a') as u:
        u.write(addText.get())
        u.write('\n')

        rootC.destroy()
        LoggedIn()

Login()

A:

I would do this way:
def LoggedIn():

    global userfile

    roots1 = Tk()
    roots1.title('Logged in successfully')
    roots1.geometry('300x300')

    userfile = nameEL.get() + '.txt'
    #and the tkinter widgets

This code userfile = open(nameEL.get() + '.txt', 'a') was a bit weird, you're using the open command to create an object that you use as if it was a string later. You only need userfile to be a string, not a command. Then, you can use it to open the file (see below)
def View():

    global userfile

    try:
        with open (userfile, 'r') as u:
            print (u.read())
    except FileNotFoundError: #file doesn't exist
        r = Tk()
        r.title('View')
        r.geometry('300x50')
        rlbl = Label(r, text='\n[!] This file doesn't exist [!]')
        rlbl.pack()
        r.mainloop()
        LoggedIn()
    except ValueError: #some error when reading
        r = Tk()
        r.title('View')
        r.geometry('300x50')
        rlbl = Label(r, text='\n[!] Problem when reading the file [!]')
        rlbl.pack()
        r.mainloop()
        LoggedIn()

Here, print(userfile.read()) was not working because, you createduserfile with append mode (maybe there was other issue too)
and finally
def Add():
    global userfile

    with open(userfile, 'a') as u:
        u.write(addText.get()) #don't forger the .get ()
        u.write('\n')

    rootC.destroy()
    LoggedIn()

And here, you are trying to write an Entry object in a file, Python doesn't like that. You just need to add .get() so that it writes what is in the Entry object addText.
There was another mistake here : when using a with () command, you don't need to close the file after, it's done automatically.
There might still be issues, but the files should work fine.
Edit:
When using a Text widget, the get() command requires more parameters than when it's only an Entry widget
You could use this:
u.write (addText.get('1.0', END))

