Here’s a line-by-line explanation of the tkinter calculator program:

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import tkinter as tk

• Purpose: Import the tkinter library for building GUI applications in Python.
• tk is used as an alias for easier access to tkinter functions and classes.

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def on_click(button_text):

• Purpose: Define a function to handle button clicks.
• button_text represents the label (e.g., “1”, “+”, “=”) of the button that was clicked.

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    if button_text == "C":
        entry.delete(0, tk.END)

• Purpose: If the “C” button is clicked, clear the entire text in the entry widget.
• entry.delete(0, tk.END) removes text from index 0 to the end.

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    elif button_text == "=":
        try:
            result = eval(entry.get())
            entry.delete(0, tk.END)
            entry.insert(tk.END, str(result))

• Purpose: If the “=” button is clicked:
  • Use the eval() function to evaluate the mathematical expression entered in the entry widget.
  • Clear the current text in the entry widget and display the result.
  • Wrap this in a try block to handle potential errors (e.g., invalid input like 5++2).

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        except Exception as e:
            entry.delete(0, tk.END)
            entry.insert(tk.END, "Error")

• Purpose: If an error occurs during evaluation (e.g., invalid expression), clear the entry and display “Error”.

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    else:
        entry.insert(tk.END, button_text)

• Purpose: For any other button (numbers or operators), append its text to the current entry.

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root = tk.Tk()
root.title("Simple Calculator")

• Purpose: Create the main application window (root) and set its title to “Simple Calculator”.

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entry = tk.Entry(root, width=20, font=("Arial", 18), borderwidth=5, justify='right')
entry.grid(row=0, column=0, columnspan=4)

• Purpose: Create an input field (entry) for user input and displaying results.
  • width=20: Specifies the width of the input field.
  • font=("Arial", 18): Sets the font and size.
  • borderwidth=5: Adds a border around the field.
  • justify='right': Aligns the text to the right.
  • grid(row=0, column=0, columnspan=4): Positions the widget in the first row and spans it across 4 columns.

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buttons = [
    "7", "8", "9", "/",
    "4", "5", "6", "*",
    "1", "2", "3", "-",
    "C", "0", "=", "+"
]

• Purpose: Define the layout of calculator buttons in a list, arranged row by row.

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row_value = 1
col_value = 0

• Purpose: Initialize the row and column positions for placing buttons in the grid.

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for button_text in buttons:
    button = tk.Button(root, text=button_text, width=5, height=2, font=("Arial", 14),
                       command=lambda text=button_text: on_click(text))
    button.grid(row=row_value, column=col_value, padx=5, pady=5)
    col_value += 1
    if col_value > 3:
        col_value = 0
        row_value += 1

• Purpose:
  • Loop through the buttons list to create a button for each item.
  • tk.Button(...): Create a button widget with specified properties:
    • text=button_text: Label the button.
    • width and height: Set button size.
    • font: Specify font style and size.
    • command: Assign the on_click function, passing the button’s label.
  • grid(row=row_value, column=col_value, padx=5, pady=5): Place the button in the grid, adding padding for spacing.
  • Increment the col_value for each button. If the column exceeds 3, reset it to 0 and move to the next row.

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root.mainloop()

• Purpose: Start the main event loop, which listens for user interactions and updates the GUI accordingly.

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Summary

1. Input Field (entry): Displays the input and output.
2. Buttons: Each button is created dynamically using a loop and added to the grid.
3. Button Logic: Depending on the button clicked, the program performs actions like clearing input, evaluating expressions, or appending characters.
4. Error Handling: Ensures invalid input doesn’t crash the program.

This program demonstrates the basics of creating interactive GUI applications with tkinter.