用户输入上的 Python3 Tkinter 名称错误（未定义）

Question

I'm getting the following error:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/tkinter/__init__.py", line 1705, in __call__
    return self.func(*args)
  File "/Users/XXXXXXXXXXXXX/Desktop/Python/Test Py/TestGUI.py", line 37, in trans1
    print(enter_principal)
NameError: name 'enter_principal' is not defined

I'm currently trying to learn python, so I'd be lying if I said I had any idea on what is going wrong. Here is my source code, trying to make a basic compound interest calculator. Getting this error when I'm trying to get an input from the user. Code:

#Importing GUI Module
import tkinter as tk
from tkinter import *

#Creating window
root = tk.Tk()

####Functions#####

#Root screen exit button
def exitroot():
    root.destroy()
    
#principal input
def principal():
    
    #Creating principal window and destroying home window
    window = tk.Tk()
    exitroot()
    
    #Creating widgets
    title_principal = tk.Label(window, text='Please enter your pricipal value: ')
    enter_principal = tk.Entry(window)
    b1 = tk.Button(window, text='Submit', command=trans1)

    title_principal.grid()
    enter_principal.grid()
    b1.grid()

def trans1():
    #temp function for testing purposes
    print(enter_principal)

####    

#CREATING HOME WINDOW WIDGETS
title_main = tk.Label(root, text="Compound Intrest Calculator", font=("Arial", 20, 'bold'))
start_button = tk.Button(root, text="Start", width='6', height='2', command=principal)
exit_button = tk.Button(root, text="Exit", width='6', height='2', command=exitroot)
credits_main = tk.Label(root, text="M.CXXXXXXXX 2020", font=("Arial", 8))

#PACKING HOME WINDOW WIDGETS VIA GRID
title_main.grid(row='0', columnspan='2')
start_button.grid(row='1', column='0')
exit_button.grid(row='1', column='1')
credits_main.grid(row='2', columnspan='2')

root.mainloop()

Any help is greatly appreciated. I apologise if my code is hard to follow or has blantant errors. I've spent some time looking for a fix but I am really struggling as none have worked.

Answer 1

You need to change

b1 = tk.Button(window, text='Submit', command=trans1)

TO:

b1 = tk.Button(window, text='Submit', command=lambda: trans1(enter_principal.get()))

The reason being is because you need to pass in the value typed into the tk.Entry by using enter_principal.get() .

Lambda allows the function to be called only when the button is pressed.(since the command contains parenthesis and so would be called automatically)

Once you've passed this in, you can then pass it into the trans1 function and print it.

def trans1(answer):
    # temp function for testing purposes
    print(answer)