What is Tkinter?

Until now, we have built command-line programs that accept input from the console.

However, users nowadays expect modern applications that they can interact with.

Tkinter is a library that enables us to build desktop apps in Python with a graphical user interface that users can interact with, unlike the command-line interface.

Tkinter is built into the standard Python library and is cross-platform, meaning that the same code will work on Windows, Mac, and Linux.

The buttons, text fields, and all the widgets built using Tkinter are rendered using native operating system elements.

Therefore, your Tkinter app will have a Windows app look on a Windows app, a Mac-like look and feel on a Mac, and so on.

Although Tkinter apps look outdated in terms of the user interface, you cannot build modern-looking apps using Tkinter.

However, for commercial desktop applications, Tkinter is lightweight, and the modern look of the application does not matter as much.

Creating a simple Tkinter window:

#import everything form tkinter
from tkinter import *
# Now in tkinter there is a class Tk
# we create an object of the class Tk()

root=Tk()
# This root is now our main window
# root is an instance of the Tk class
# run the code and nothing will happen
# because tkinter craetes the window and it closes in a flash
# hence to keep the window running, we use mainloop method.
# as the name implies, it will loop forever until the user exits
# the window 
root.mainloop()

Tkinter window with "Hello World" displayed on it:

from tkinter import *

root=Tk()
hello = Label(root,text="hello world")
#this won't do anything, just create a label
#after creating a label, we need to add it.
hello.pack()
# When you pack a widget into a window, tkinter resizes the window
# to be as small as it can be to fit all the widgets it has.
root.mainloop()

You can also set the size of the window:

root.geometry("300x400")

Configuring the Label widget using parameters:

hello = Label(root,text="hello world",font=("Arial", 16), fg="red", bg="white")

Creating a button widget in Tkinter:

button = Button(root,text="Click here")
button.pack()

When you click this nothing happens.

To handle a click event on a button, we need to use a proerty called command.

button = Button(root,text="Click here",command=display)

Define the display function at the top before the root=Tk()

i.e before the Tkinter loop starts.

def display():
    print('This is a display message')

Tkinter app to accept user Input:

In tkinter, we use the Entry widget to accept any input from the user.

from tkinter import *

def display():
    print(entry.get())

root=Tk()
hello = Label(root,text="Enter some text")
hello.pack()

entry = Entry(root)
entry.pack()
button = Button(root,text="Click here",command=display)
button.pack()

root.geometry("300x400")
root.mainloop()

Tkinter program to accept two numbers and add them:

from tkinter import *

def add():
    n1 = int(number1.get())
    n2 = int(number2.get())
    print(n1+n2)

root=Tk()
hello = Label(root,text="Enter some text")
hello.pack()

number1 = Entry(root)
number1.pack()

number2= Entry(root)
number2.pack()
button = Button(root,text="Click here",command=add)
button.pack()

root.geometry("300x400")
root.mainloop()

Lets display the number onto a label

from tkinter import *

def add():
    n1 = int(number1.get())
    n2 = int(number2.get())
# new code added
    result = str(n1+n2)
    answer.config(text="Answer is: "+ result)
# new code added
root=Tk()
hello = Label(root,text="Enter some text")
hello.pack()

number1 = Entry(root)
number1.pack()

number2= Entry(root)
number2.pack()
button = Button(root,text="Click here",command=add)
button.pack()

# new code added
answer = Label(root)
answer.pack()
# new code added

root.geometry("300x400")
root.mainloop()

Checkboxes in Tkinter:

Checkboxes in Tkinter are called as check button.

Checkboxes are used to show multiple options to user.

User can select multiple options from checkboxes.

Example:

from tkinter import *

def selected():
    label.config(text=var.get())

root=Tk()
# create a variable to store checkbox state
var = BooleanVar()
checkbox = Checkbutton(root,text ="Accept terms", variable=var, command=selected)
checkbox.pack()

label=Label(root)
label.pack()
root.geometry("300x400")
root.mainloop()

Frames in Tkinter:

Frame is a widget that allows you to organize the layout of other widgets.

Let's create a frame and add widgets to it. A frame is like a container that will hold all our widgets. Therefore, a window is also a container, and inside a window, we will add a frame. On that frame, we will add widgets.

A frame allows you to group together widgets of the same type. Let's take the boilerplate code and understand how frames are created.

from tkinter import *

root = Tk()
root.geometry("300x400")

# create a frame object
frame = Frame(root)
frame.pack()

# now let's create another frame
frame2 = Frame(root)
frame2.pack()

# now let's create some widgets and add them to a frame
# instead of adding it to the root window, we will pass frame here
button1 = Button(frame, text="Button1")
button2 = Button(frame2, text="button2")

# we still need to pack these buttons
button1.pack()
button2.pack()

root.mainloop()

Now let's change the layout of one of the frames. Let's say you want to place that frame at the bottom of the window. Here is how to do it:

frame2.pack(side=BOTTOM)

This places frame2 and all the elements inside it at the very bottom of the window.

Grid layout manager:

A grid is nothing but a set of rows and columns.

When you want to place widgets inside of a window, you simply specify the rows and columns for that widget.

Lets create a basic form with two labels and two textFields and place them in a form like manner using grid layout.

from tkinter import *

root=Tk()

label1 = Label(root,text='Email')
label2 = Label(root,text="Password")

text1 = Entry(root)
text2 = Entry(root)

label1.grid(row=0,column=0)
label2.grid(row=1,column=0)

text1.grid(row=0,column=1)
text2.grid(row=1,column=1)

button = Button(root,text='Login')
button.grid(row=2,column=1)
root.geometry("300x400")
root.mainloop()

OOP way of writing Tkinter app:

Previously we were creating the root window and then adding widgets and frames on top of it.

Same can be done using OOP as well.

Lets create user interface having a window and two buttons which perform some functions.

from tkinter import *

class Demo:
    # init method to initialize the window object
    # we have passed in rootone which is the root
    # rootone is simply the name of parameter passed to init

    def __init__(self,rootone):
        #This will contain the code used to setup our window
        # lets add a frame on the root window
        frame = Frame(rootone)
        frame.pack()
        #as this is a class instead of saying printbutton we use self

        self.printbutton = Button(frame,text='Click Here',command=self.printmessage)
        self.printbutton.pack()

        #frame.quit is a built-in method to close a window
        self.quitbutton = Button(frame,text='Exit',command=frame.quit)
        self.quitbutton.pack()

    #now let's define the method printmessage here
    def printmessage(self):
        print("Button Clicked!")
    # now once class is created, we create an object out of it

root=Tk()
# create an object of the above class
# pass in this above root to the class
b = Demo(root)

root.mainloop()