Python-如何从 tkinter 小部件获取值并将其分配给变量

Question

from tkinter import *
import tkinter as tk
import pyodbc

root1 = tk.Tk()

label1 = tk.Label(root1, text='product A')
entry1 = tk.Entry(root1)

label1.pack(side = tk.TOP)
entry1.pack()
input1= StringVar()
input1.set(entry1.get())
print (input1)

This code is used to assign the value from the input textbox widget to a variable-Input1. However,the value I get is:PY_VAR0 instead of the text in Entry1.

I need to print the input text. Why is PY_VAR0 appearing?

Please help.

Thank you.

Answer 1

The problem is that you're getting the value of the entry widget before the user has a chance to type anything, so it will always be the empty string.

If you wait to do the get until after the user enters something, your code will work fine as-is. Though, I don't see any reason to use a StringVar as it just adds an extra object that serves no real purpose. There's no reason to use a StringVar with an entry widget unless you need the extra features that a StringVar gets you -- namely, variable traces.

The reason you are seeing PY_VAR0 is because you must use the get method to get the value out of an instance of StringVar . Change your statement to print input1.get() .

Answer 2

To get the contents of a StringVar call get() :

input1.get()

Also, you should bind your StringVar to the Entry otherwise the StringVar won't change with the contents of the Entry widget:

entry1.config(textvariable=input1) 

Or you can bind at construction:

input1 = StringVar()
entry1 = tk.Entry(root1, textvariable=input1)

Answer 3

If you want to print the value of a Tkinter variable, you must use the .get() method to retrieve it, as in

print(input1.get())

Otherwise, you are accessing the variable's name, which is what you're seeing.

When you have a StringVar (or other similar Tkinter variable), you can get the name of the variable by casting to a string, such as

my_string_variable_name = str(input1)

This is the easiest way to get the variable name if you didn't set it when creating the variable. You can set a variable name as follows:

sv = tkinter.StringVar(name='Fred', value='Flintstone') # Note you can set a value, too!

Then

print(str(sv)) # which is what is happening when you say print(sv)

prints out 'Fred', and

print(sv.get())

prints out 'Flintstone'