How to configure Frame widget in Tkinter?

It is a very common error in Tkinter. The problem is the use of grid, placeor packon the same line where the widget is instantiated. It's very good to save lines but sometimes it has its consequences ツ.

If this is done:

mainframe = ttk.Frame(root, ).grid()

mainframeis not an object ttk.Frame, it is the return of the method grid, which does not return anything ( None). That's why the error says:

TypeError: 'NoneType' object does not support item assignment

If you want to use the name of the object to change its attributes later, you need to separate the instance from the method call grid:

mainframe = ttk.Frame(root)
mainframe.grid()

You can see the difference by doing something as simple as printing the mainframe variable in both cases:

import tkinter as tk
from tkinter import ttk

root=tk.Tk()

mainframe0 = ttk.Frame(root).grid()
print(type(mainframe0))

mainframe1 = ttk.Frame(root)
mainframe1.grid()
print(type(mainframe1))

In the output we see the difference:

>>> <class 'NoneType'>
>>> <class 'tkinter.ttk.Frame'>

Exactly the same problem occurs when trying to chain the widget's method calls:

Entry(...).grid(...).config(..)

In this case the error and the problem are identical, Entry()create an object of the class Entry, then .grid()call the method gridof the object, so far so good. Then it .config()tries to call the config grid output( None) method and here we have the same problem as before. For the above to work, each method should return a reference to the object to which it belongs, that is, it can gridreturn a reference to the object created with Entry()and not None. The solution is the same:

entry = Entry(...)
entry.grid(...)
entry.config(...)

If we never need to refer to the widget again, it is correct to apply the method on the same line, but in this case a variable should not be associated with the output, since we will have a lot of variables, all associated with Noneand totally useless. instead of doing:

button = tk.Button().grid()
label = tk.Label().grid()

we just have to do:

tk.Button().grid()
tk.Label().grid()

On the other hand, it is not an error per se, but a very bad practice that for some reason is very widespread in Tkinter tutorials, you should never import a module in Python in the way (except justified cases, mainly to merge two spaces of Names):

from tkinter import *

Your code is simple and will not give you problems at first but it can cause a lot of headaches when using complex modules or in medium-sized projects. This form of import exposes all module identifiers in your current namespace. In principle you don't know the name of all the classes, objects or functions that the module contains, so you can end up overwriting your own functions in your Tkinter functions namespace or vice versa without realizing it. On the other hand, it makes it difficult for third parties to read the code ("Explicit better than implicit").

The proper way is to use one of these:

from tkinter import Tk, Button, Frame...
import tkinter
import tkinter as tk

Your code could look like this:

import tkinter as tk
from tkinter import ttk

root=tk.Tk()

mainframe = ttk.Frame(root)
mainframe.grid()
mainframe['padding'] = 5, 10

etiqueta = ttk.Label(root, text="try")
etiqueta.grid(row=0, column=2)

buton=ttk.Button(mainframe, text="push here", command=root.quit)
buton.grid(row=1, column=24)

root.mainloop()

Result:

Edition:

The parameters weidhtand heightare specified the same as the rest, with the exception that if we want to avoid the automatic adjustment carried out by the layout and that the widget is forced to take those measures, we need to use the method together:grid_propagate()

import tkinter as tk
from tkinter import ttk

root=tk.Tk()

mainframe = ttk.Frame(root)
mainframe.grid()
mainframe['padding'] = 5, 10
mainframe['width'] = 100
mainframe['height'] = 100
mainframe.grid_propagate(0)

etiqueta = ttk.Label(root, text="try")
etiqueta.grid(row=0, column=2)

buton=ttk.Button(mainframe, text="push here", command=root.quit)
buton.grid(row=1, column=24)

root.mainloop()