In this article, we’ll show you how to build a functional calculator GUI using Python and Tkinter. Tkinter is a standard library module that provides a simple way to create graphical user interfaces (GUIs) with Python. A calculator GUI is a useful example to demonstrate how to use Tkinter widgets, such as buttons, labels, and entry fields, to create an interactive application.

The steps to create a Python calculator GUI are:

  1. Import the Tkinter module and create a root window.
  2. Create a frame to hold the calculator display and buttons.
  3. Create a label to show the calculator expression and result.
  4. Create a string variable to store the calculator expression and result.
  5. Create a function to update the label with the string variable.
  6. Create a function to clear the string variable and reset the label.
  7. Create a function to append a character to the string variable and update the label.
  8. Create a function to evaluate the string variable as a mathematical expression and update the label with the result or an error message.
  9. Create buttons for digits, operators, decimal point, equal sign, and clear sign, and bind them to the corresponding functions.
  10. Arrange the buttons in a grid layout inside the frame.
  11. Format the buttons so they look nice.
  12. Bind keyboard keys to the calculator buttons.
  13. Run the main loop of the root window.

As a demonstration of what Tkinter is capable of, we’ve created a calculator GUI that accomplishes each of the steps above, including binding keyboard keys to the Tkinter calculator buttons. The code for the calculator GUI is:

# Import Tkinter module
import tkinter as tk

# Create root window
root = tk.Tk()

# Create frame
frame = tk.Frame(root)

# Create label
label = tk.Label(frame, text="0", font=("Arial", 20), bg="white", width=15)
label.grid(row=0, column=0, columnspan=4)

# Create string variable
string_var = tk.StringVar()

# Create update function
def update_label():

# Create clear function
def clear():

# Create append function
def append(char):
    if string_var.get() == "0":
        string_var.set(string_var.get() + char)

# Create evaluate function
def evaluate():
        result = eval(string_var.get())

# Create buttons
button_1 = tk.Button(frame, text="1", font=("Arial", 15), command=lambda: append("1"))
button_2 = tk.Button(frame, text="2", font=("Arial", 15), command=lambda: append("2"))
button_3 = tk.Button(frame, text="3", font=("Arial", 15), command=lambda: append("3"))
button_4 = tk.Button(frame, text="4", font=("Arial", 15), command=lambda: append("4"))
button_5 = tk.Button(frame, text="5", font=("Arial", 15), command=lambda: append("5"))
button_6 = tk.Button(frame, text="6", font=("Arial", 15), command=lambda: append("6"))
button_7 = tk.Button(frame, text="7", font=("Arial", 15), command=lambda: append("7"))
button_8 = tk.Button(frame, text="8", font=("Arial", 15), command=lambda: append("8"))
button_9 = tk.Button(frame, text="9", font=("Arial", 15), command=lambda: append("9"))
button_0 = tk.Button(frame, text="0", font=("Arial", 15), command=lambda: append("0"))
button_plus = tk.Button(frame, text="+", font=("Arial", 15), command=lambda: append("+"))
button_minus = tk.Button(frame, text="-", font=("Arial", 15), command=lambda: append("-"))
button_multiply = tk.Button(frame, text="*", font=("Arial", 15), command=lambda: append("*"))
button_divide = tk.Button(frame, text="/", font=("Arial", 15), command=lambda: append("/"))
button_point = tk.Button(frame, text=".", font=("Arial", 15), command=lambda: append("."))
button_equal = tk.Button(frame, text="=", font=("Arial", 15), command=evaluate)
button_clear = tk.Button(frame, text="C", font=("Arial", 15), command=clear)

# Arrange buttons in grid layout
button_1.grid(row=1, column=0)
button_2.grid(row=1, column=1)
button_3.grid(row=1, column=2)
button_plus.grid(row=1, column=3)
button_4.grid(row=2, column=0)
button_5.grid(row=2, column=1)
button_6.grid(row=2, column=2)
button_minus.grid(row=2, column=3)
button_7.grid(row=3, column=0)
button_8.grid(row=3, column=1)
button_9.grid(row=3, column=2)
button_multiply.grid(row=3, column=3)
button_0.grid(row=4, column=0)
button_point.grid(row=4, column=1)
button_equal.grid(row=4, column=2)
button_divide.grid(row=4, column=3)
button_clear.grid(row=5, column=0, columnspan=4)

#format buttons
button_1.config(width=5, height=2)
button_2.config(width=5, height=2)
button_3.config(width=5, height=2)
button_4.config(width=5, height=2)
button_5.config(width=5, height=2)
button_6.config(width=5, height=2)
button_7.config(width=5, height=2)
button_8.config(width=5, height=2)
button_9.config(width=5, height=2)
button_0.config(width=5, height=2)
button_plus.config(width=5, height=2)
button_minus.config(width=5, height=2)
button_multiply.config(width=5, height=2)
button_divide.config(width=5, height=2)
button_point.config(width=5, height=2)
button_equal.config(width=5, height=2)
button_clear.config(width=21, height=2)

#add keyboard shortcuts to calculator buttons
root.bind("<Return>", lambda event: evaluate())
root.bind("<KP_Enter>", lambda event: evaluate())
root.bind("<BackSpace>", lambda event: clear())
root.bind("1", lambda event: append("1"))
root.bind("2", lambda event: append("2"))
root.bind("3", lambda event: append("3"))
root.bind("4", lambda event: append("4"))
root.bind("5", lambda event: append("5"))
root.bind("6", lambda event: append("6"))
root.bind("7", lambda event: append("7"))
root.bind("8", lambda event: append("8"))
root.bind("9", lambda event: append("9"))
root.bind("0", lambda event: append("0"))
root.bind("+", lambda event: append("+"))
root.bind("-", lambda event: append("-"))
root.bind("*", lambda event: append("*"))
root.bind("/", lambda event: append("/"))
root.bind(".", lambda event: append("."))
root.bind("<Escape>", lambda event: root.destroy())

# Start main loop

When you run this program, you’ll get a simple, but beautiful, Python calculator like this one:

Python Calculator GUI with Tkinter

I encourage you to take a look through the code and see if there are ideas you can use to add to your next Tkinter project. I hope you have learned something useful from this Tkinter code example. Feel free to subscribe below for more helpful Python tutorials.

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