In today’s article, we are going to create a simple calculator that calculates interest using the tkinter library, where the user can input their data and, by just clicking the calculate button, receive the calculated interest. This builds upon our previous exploration of crafting a codebase for a simple calculator using the tkinter library in Python. Without further ado, let’s dive into how we can extend that basic calculator into a more functional application that can handle interest calculations.
Table of Contents
- Necessary Libraries
- Imports
- Class Definition
- Initializer Method
- Setting up the Window
- Creating Labels
- Placing the Labels on the Window
- Creating Variables to Hold User Input
- Creating Entry Widgets
- Placing Entry Widgets and Adding the Result Label
- Creating Buttons
- Calculate Function
- Clear_entries Function
- Setting up the Main Window
- Example
- Full Code
Necessary Libraries
For this code to work correctly, it’s necessary to install the tkinter library through the terminal or command prompt.
$ pip install tk
Imports
from tkinter import *
First, we import everything from the tkinter library, allowing us to use the graphical user interface (GUI).
Class Definition
class SimpleInterestCalculator:
Then we create a class basically the blueprint for our interest Calculator.
Initializer Method
def __init__(self, master):
What we did here is start with the setup phase which is a set of instructions that prepare the setup of the window.
Setting up the Window
self.master = master
master.title("Simple Interest Calculator - The Pycodes")
master.geometry("500x300")
Here, we gave our interest Calculator a name and defined its geometry.
Creating Labels
self.principal_label = Label(master, text="Principal:", font="arial 15")
self.rate_label = Label(master, text="Rate Of Interest:", font="arial 14")
self.time_label = Label(master, text="Time:", font="arial 15")
self.interest_label = Label(master, text="Interest:", font="arial 15")
After that, we give Labels in other words, we create name tags in a specific font.
Placing the Labels on the Window
self.principal_label.place(x=50, y=20)
self.rate_label.place(x=50, y=90)
self.time_label.place(x=50, y=160)
self.interest_label.place(x=50, y=230)
The code presented here basically tells the computer where to put the name tags that we created.
Creating Variables to Hold User Input
self.principal_value = StringVar()
self.rate_value = StringVar()
self.time_value = StringVar()
In this part, we create a number of containers where the user’s input is held.
Creating Entry Widgets
self.principal_entry = Entry(master, textvariable=self.principal_value, font="arial 20", width=8)
self.rate_entry = Entry(master, textvariable=self.rate_value, font="arial 20", width=8)
self.time_entry = Entry(master, textvariable=self.time_value, font="arial 20", width=8)
Next, we create Entry boxes where the user can type his input.
Placing Entry Widgets and Adding the Result Label
self.principal_entry.place(x=200, y=20)
self.rate_entry.place(x=200, y=90)
self.time_entry.place(x=200, y=160)
self.result_label = Label(master, text="", font="arial 30 bold")
self.result_label.place(x=200, y=220)
This code informs the computers where to put the entry boxes, as well as creates the result label where the result of the calculation will appear and chooses a place for it.
Creating Buttons
self.calculate_button = Button(master, text="Calculate", font="arial 15", command=self.calculate)
self.calculate_button.place(x=350, y=20)
self.clear_button = Button(master, text="Clear", font="arial 15", command=self.clear_entries)
self.clear_button.place(x=350, y=90)
self.exit_button = Button(master, text="Exit", command=master.destroy, font="arial 15", width=8)
self.exit_button.place(x=350, y=160)
Following that, we create three buttons once clicked each one of them triggers something, the first button is “Calculate” which calls the calculate function, the second one is called “Clear” which calls the clear_entries function, the last one is called “Exit” which as the name suggests Exit the window.
Calculate Function
def calculate(self):
try:
principal = float(self.principal_value.get())
rate = float(self.rate_value.get())
time = float(self.time_value.get())
amount = (principal * rate * time) / 100
self.result_label.config(text=f"{amount}")
except ValueError:
self.result_label.config(text="Invalid input. Please enter valid numbers.")
Then, we define a function that gets triggered once the user clicks the “Calculate” button, what this function does is ensure the numbers inputted by the user are converted to floats for the amount calculation, if there is a conversion issue, an error message appears giving feedback to the user. If not, the calculated interest amount appears on the result label.
Clear_entries Function
def clear_entries(self):
self.principal_value.set("")
self.rate_value.set("")
self.time_value.set("")
self.result_label.config(text="")
Here, we created a function that gets triggered once the user clicks the “Clear” button, what this function does is simply set the principal, rate, and time entry widgets to their initial states and also clear the result label.
Setting up the Main Window
if __name__ == "__main__":
root = Tk()
app = SimpleInterestCalculator(root)
root.mainloop()
Lastly, this part creates the main window and keeps it in a loop (open) until the user chooses to exit the said window.
Example
Full Code
from tkinter import *
class SimpleInterestCalculator:
def __init__(self, master):
self.master = master
master.title("Simple Interest Calculator - The Pycodes")
master.geometry("500x300")
self.principal_label = Label(master, text="Principal:", font="arial 15")
self.rate_label = Label(master, text="Rate Of Interest:", font="arial 14")
self.time_label = Label(master, text="Time:", font="arial 15")
self.principal_label.place(x=50, y=20)
self.rate_label.place(x=50, y=90)
self.time_label.place(x=50, y=160)
self.interest_label = Label(master, text="Interest:", font="arial 15")
self.interest_label.place(x=50, y=230)
self.principal_value = StringVar()
self.rate_value = StringVar()
self.time_value = StringVar()
self.principal_entry = Entry(master, textvariable=self.principal_value, font="arial 20", width=8)
self.rate_entry = Entry(master, textvariable=self.rate_value, font="arial 20", width=8)
self.time_entry = Entry(master, textvariable=self.time_value, font="arial 20", width=8)
self.principal_entry.place(x=200, y=20)
self.rate_entry.place(x=200, y=90)
self.time_entry.place(x=200, y=160)
self.result_label = Label(master, text="", font="arial 30 bold")
self.result_label.place(x=200, y=220)
self.calculate_button = Button(master, text="Calculate", font="arial 15", command=self.calculate)
self.calculate_button.place(x=350, y=20)
self.clear_button = Button(master, text="Clear", font="arial 15", command=self.clear_entries)
self.clear_button.place(x=350, y=90)
self.exit_button = Button(master, text="Exit", command=master.destroy, font="arial 15", width=8)
self.exit_button.place(x=350, y=160)
def calculate(self):
try:
principal = float(self.principal_value.get())
rate = float(self.rate_value.get())
time = float(self.time_value.get())
amount = (principal * rate * time) / 100
self.result_label.config(text=f"{amount}")
except ValueError:
self.result_label.config(text="Invalid input. Please enter valid numbers.")
def clear_entries(self):
self.principal_value.set("")
self.rate_value.set("")
self.time_value.set("")
self.result_label.config(text="")
if __name__ == "__main__":
root = Tk()
app = SimpleInterestCalculator(root)
root.mainloop()
Happy Coding!
Learn also: How to Make a Simple Calculator using Python tkinter
