Why is Tkinter Entry's get function returning nothing?

Question

I'm trying to use an Entry field to get manual input, and then work with that data.

All sources I've found claim I should use the get() function, but I haven't found a simple working mini example yet, and I can't get it to work.

I hope someone can tel me what I'm doing wrong. Here's a mini file:

from tkinter import *


master = Tk()

Label(master, text="Input: ").grid(row=0, sticky=W)

entry = Entry(master)
entry.grid(row=0, column=1)

content = entry.get()
print(content)  # does not work

mainloop()

This gives me an Entry field I can type in, but I can't do anything with the data once it's typed in.

I suspect my code doesn't work because initially, entry is empty. But then how do I access input data once it has been typed in?

Solution 1

It looks like you may be confused as to when commands are run. In your example, you are calling the get method before the GUI has a chance to be displayed on the screen (which happens after you call mainloop.

Try adding a button that calls the get method. This is much easier if you write your application as a class. For example:

import tkinter as tk

class SampleApp(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)
        self.entry = tk.Entry(self)
        self.button = tk.Button(self, text="Get", command=self.on_button)
        self.button.pack()
        self.entry.pack()

    def on_button(self):
        print(self.entry.get())

app = SampleApp()
app.mainloop()

Run the program, type into the entry widget, then click on the button.

Solution 2

You could also use a StringVar variable, even if it's not strictly necessary:

v = StringVar()

e = Entry(master, textvariable=v)
e.pack()

v.set("a default value")
s = v.get()

For more information, see this page on effbot.org.

Solution 3

A simple example without classes:

from tkinter import *    
master = Tk()

# Create this method before you create the entry
def return_entry(en):
    """Gets and prints the content of the entry"""
    content = entry.get()
    print(content)  

Label(master, text="Input: ").grid(row=0, sticky=W)

entry = Entry(master)
entry.grid(row=0, column=1)

# Connect the entry with the return button
entry.bind('<Return>', return_entry) 

mainloop()

Solution 4

*

master = Tk()
entryb1 = StringVar

Label(master, text="Input: ").grid(row=0, sticky=W)

Entry(master, textvariable=entryb1).grid(row=1, column=1)

b1 = Button(master, text="continue", command=print_content)
b1.grid(row=2, column=1)

def print_content():
    global entryb1
    content = entryb1.get()
    print(content)

master.mainloop()

What you did wrong was not put it inside a Define function then you hadn't used the .get function with the textvariable you had set.

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Comments

[Russell Smith]

In your example, what exactly are you expecting? You haven't given the entry widget any text before you call get so of course it returns an empty string.

[Russell Smith]

A StringVar isn't necessary, strictly speaking. They are handy, but for this question they are completely superfluous.

[CodingCat]

Ah, I see. I'm not really firm on classes yet (still very much a beginner at programming in general), but I see the problem. I'll just make an "Analyze!" button and put the get()-function in there, that should work. Thank you!

[Deep-B]

You might need to add self as a parameter while calling the superclass init: tk.Tk.__init__(self). Otherwise, very useful example!

[Deep-B]

And, er, you misspelt app in the last line. <_<"