“TypeError: Can't convert 'NoneType' object to str implicitly” when var should have a value

问题

import sys
from tkinter import *
def print():
    print("Encoded " + message + " with " + offset)

gui = Tk()

gui.title("Caesar Cypher Encoder")

Button(gui, text="Encode", command=encode).grid(row = 2, column = 2)
Label(gui, text = "Message").grid(row = 1, column =0)
Label(gui, text = "Offset").grid(row = 1, column =1)
message = Entry(gui).grid(row=2, column=0)
offset = Scale(gui, from_=0, to=25).grid(row=2, column=1)

mainloop( )

When i run this code with an input in both the input box and a value on the slider - it comes up with the error

>>>Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Python34\lib\tkinter\__init__.py", line 1533, in __call__
return self.func(*args)
File "C:/Users/xxxx/Desktop/Code/Functionised/GUI.pyw", line 5, in encode
print("Encoded " + message + " with " + offset)
TypeError: Can't convert 'NoneType' object to str implicitly

using a simple str() does not work by the way

EDIT

With the new code

import sys
from tkinter import *
def printer():
    print(message)
    print(offset)

gui = Tk()

gui.title("Caesar Cypher Encoder")

Button(gui, text="Encode", command=printer).grid(row = 2, column = 2)
Label(gui, text = "Message").grid(row = 1, column =0)
Label(gui, text = "Offset").grid(row = 1, column =1)
message = Entry(gui)
message.grid(row=2, column=0)
offset = Scale(gui, from_=0, to=25)
offset.grid(row=2, column=1)

mainloop( )

It returns

.46329264
.46329296

EDIT 2

def printer():
    print(message.get())
    print(offset.get())

this fixes the .xxxxxxxx problem

回答1:

In answer to your first edit - the .get() command should be the most useful

Use it in the form of

print(message.get())

rather than

print(message)

回答2:

You are setting the variables message and offset to widgets but then you position them on the same line, this makes them Nonetype objects, instead position them on the next line e.g.:

message = Entry(gui)
message.grid(row=2, column=0)
offset = Scale(gui, from_=0, to=25)
offset.grid(row=2, column=1)

this should solve your problem, but also, it's not advised to use from tkinter import * rather import tkinter as tk, and your function print() should be differently named (not the same as a python keyword) so that it is less confusing and prevents errors, make it printer() or similar to be on the safe side.

Hope this helps you!

来源：https://stackoverflow.com/questions/26822410/typeerror-cant-convert-nonetype-object-to-str-implicitly-when-var-should-h

标签

python

tkinter

python-3.4