2. Label textvariable: toggle text

See: https://www.geeksforgeeks.org/python-setting-and-retrieving-values-of-tkinter-variable/

2.1. Toggle text via button

../_images/toggle_text_1.png ../_images/toggle_text_2.png
The code below creates a Tkinter GUI application that toggles text on a label when a button is clicked:

  1. A StringVar is created to hold the label's text: text_var = tk.StringVar().

  2. The set method initializes the text: text_var.set("Initial Text").

  3. The get method retrieves the current text: current_value = text_var.get().

  4. A label is associated with the StringVar: label = tk.Label(root, textvariable=text_var).

  5. A button is created with a command to toggle the text: button = tk.Button(root, command=update_text).

  6. The update_text function checks the current value of text_var and toggles it using set.

  7. Clicking the button triggers the command to update the label's text.

2.1.1. Required Syntax

class StringVar
Syntax: text_var = tk.StringVar()
Description: Creates a Tkinter variable for holding string data.
Default: None
Example: text_var = tk.StringVar()
set()
Syntax: text_var.set("New Value")
Description: Sets the value of the StringVar to the specified string.
Default: None
Example: text_var.set("Hello, World!")
get()
Syntax: current_value = text_var.get()
Description: Retrieves the current value of the StringVar.
Default: None
Example: current_value = text_var.get()
textvariable
Syntax: label_widget = tk.Label(parent, textvariable=variable)
Description: Associates a Tkinter variable with the label text. If the variable is changed, the label text is updated.
Default: None
Example: label_widget = tk.Label(root, textvariable=my_var)
command
Syntax: button_widget = tk.Button(parent, command=callback_function)
Description: Specifies the function to be called when the button is clicked.
Default: None
Example: button_widget = tk.Button(root, command=on_click)

2.1.2. Code features

Here's a breakdown of the main parts of the code:

  1. Create a variable: StringVar:

    • text_var = tk.StringVar(): Creates a StringVar instance, text_var, which is a special tkinter variable for holding string data.

    • text_var.set("Initial Text"): Sets the initial value of text_var.

  2. Link variable to Label with textvariable:

    • label = tk.Label(root, textvariable=text_var, font=("Helvetica", 16)): Creates a label in the window root.

    • The textvariable parameter is linked to text_var, so the label text displays text_var's value.

  3. Define the Function:

    • def update_text(): Defines a function, update_text, that gets text_var's current value using text_var.get().

    • It toggles text_var between "Initial Text" and "Updated Text" by using text_var.set().

  4. Set Button command:

    • button = tk.Button(root, text="Toggle Text", command=update_text): Creates a button with the label "Toggle Text" and sets update_text as the function that runs when clicked.

2.1.3. Code

This code creates a basic GUI with a button that toggles the text of a label.
import tkinter as tk


# Function to update the text
def update_text():
    if text_var.get() == "Initial Text":
        text_var.set("Updated Text")
    else:
        text_var.set("Initial Text")


# Create the main window
root = tk.Tk()
root.geometry("300x100")
root.title("Toggle Text")

# Create a StringVar to hold the text
text_var = tk.StringVar()
text_var.set("Initial Text")

# Create a Label widget with textvariable
label = tk.Label(root, textvariable=text_var, font=("Helvetica", 16))
label.pack(pady=10)

# Create a Button to trigger the text update
button = tk.Button(root, text="Toggle Text", command=update_text)
button.pack(pady=10)

# Run the application
root.mainloop()

Tasks

  1. Write code to reverse a string entered by a user into an entry field, using an input_var and an output_var.
    ../_images/reverse_string.png
  2. Modify the previous answer to insert a random palindrome if the entry string is blank.
    ../_images/reverse_string_palindromes.png

Write code to reverse a string entered by a user into an entry field, using an input_var and an output_var.

import tkinter as tk


# Function to transform the text
def transform_text():
    user_input = input_var.get()
    if user_input:
        # reverse
        reversed_text = user_input[::-1]
        output_var.set(reversed_text)
    else:
        output_var.set("Please enter a string.")


# Create the main window
root = tk.Tk()
root.geometry("300x200")
root.title("String Reverser")

# Create a StringVar to hold the user input
input_var = tk.StringVar()

# Create a Label and Entry for user input
input_label = tk.Label(root, text="Enter a string:", font=("Helvetica", 12))
input_label.pack(pady=5)
input_entry = tk.Entry(root, textvariable=input_var, font=("Helvetica", 12))
input_entry.pack(pady=5)

# Create a Button to trigger the text Reversal
button = tk.Button(root, text="Reversed Text", command=transform_text)
button.pack(pady=5)

# Create a StringVar to hold the transformed text
output_var = tk.StringVar()
output_var.set("")

# Create a Label widget with textvariable for the output
output_result = tk.Label(root, textvariable=output_var, font=("Helvetica", 12))
output_result.pack(pady=5)

# Run the application
root.mainloop()

Modify the previous answer to insert a random palindrome if the entry string is blank.

import tkinter as tk
import random

# List of palindromes
palindromes = [
    "aibohphobia", "civic", "deified", "kayak", "level", "madam", "minim", "noon",
    "racecar", "radar", "refer", "repaper", "reviver", "rotator", "rotor", "sagas",
    "solos", "stats", "tenet", "wow"
]


# Function to transform the text
def transform_text():
    user_input = input_var.get()
    if user_input:
        # Reverse the user input
        reversed_text = user_input[::-1]
        output_var.set(reversed_text)
    else:
        # Use a random palindrome if no input is provided
        random_palindrome = random.choice(palindromes)
        input_var.set(random_palindrome)
        output_var.set(random_palindrome)


# Create the main window
root = tk.Tk()
root.geometry("300x200")
root.title("String Reverser")

# Create a StringVar to hold the user input
input_var = tk.StringVar()

# Create a Label and Entry for user input
input_label = tk.Label(root, text="Enter a string:", font=("Helvetica", 12))
input_label.pack(pady=5)
input_entry = tk.Entry(root, textvariable=input_var, font=("Helvetica", 12))
input_entry.pack(pady=5)

# Create a Button to trigger the text reversal
button = tk.Button(root, text="Reverse Text", command=transform_text)
button.pack(pady=20)

# Create a StringVar to hold the transformed text
output_var = tk.StringVar()
output_var.set("")

# Create a Label widget with textvariable for the output
output_result = tk.Label(root, textvariable=output_var, font=("Helvetica", 12))
output_result.pack(pady=5)

# Run the application
root.mainloop()