## Using a Calculator App is Easy

Using a calculator app is a fundamental task that anybody must perform at least once in a while. However, creating one may seem like an overwhelming task, especially for beginners.

Here’s the good news: building a calculator app is easier than you think, and with the help of Streamlit, a powerful Python library, it is achievable in just a couple of hours. Not only is building a calculator app fun and exciting, but it is also an excellent way to hone your coding skills.

In this tutorial, we’ll look at how to create a calculator app in Python using Streamlit.

## Importance of Practice

Before diving into the nitty-gritty details of building a calculator app, let’s take a moment to appreciate the importance of practice. Practice is the key to mastering any skill, and coding is no exception.

Regular practice helps you become comfortable with your tools and libraries, which, in turn, enables you to write efficient code. In the long run, this results in quicker development and more robust applications.

If you’re new to coding, don’t be afraid to make mistakes or try out new things. The more you code, the more you learn.

## Overview of the Tutorial Series

### 1. Setting up the Python File and Importing Streamlit

In this tutorial series, we will explore how to create a calculator app using the Streamlit library. Streamlit is a powerful Python library that allows you to build interactive web applications with ease.

In the first tutorial, we’ll cover how to set up the Python file and import Streamlit. We will also add a title and a horizontal line to our calculator app.

### 2. Adding Calculator Buttons and Performing Basic Calculations

In the next tutorial, we’ll add calculator buttons and perform basic calculations. In the final tutorial, we’ll look at how to add advanced features, such as scientific calculator functionality.

## Reminder to go Through Previous Tutorials

If you’re new to Streamlit, we recommend that you go through the previous tutorials in this series to get a better understanding of how to use the library. In the first tutorial, we covered how to install Streamlit and create a simple “Hello, World!” app.

In the second tutorial, we explored how to create a basic web form that allows users to input their names. Going through these tutorials will provide you with a solid foundation that you can build upon as we dive into building a calculator app.

## Creating the Basic App

Now that we’ve covered the importance of practice and provided an overview of the tutorial series let’s dive into creating our basic calculator app using Streamlit.

### Setting up the Python file and Importing Streamlit

The first step in building a calculator app is setting up the Python file and importing the Streamlit library. To achieve this, we’ll create a new Python file and install Streamlit using pip.

Once the installation is complete, we’ll import the library into our Python file using the following code:

`import streamlit as st`

### Adding a Title and Horizontal Line

Now that we have Streamlit set up in our Python file, the next step is to add a title and a horizontal line to our calculator app. To achieve this, we’ll use the `st.title()` and `st.hr()` functions, respectively.

The `st.title()` function adds a large title at the top of our app, while the `st.hr()` function adds a horizontal line underneath the title. Here’s the code:

```
st.title("Basic Calculator App")
st.hr()
```

## Conclusion

In conclusion, practicing coding is essential to become proficient at it. Building a calculator app is an excellent way to exercise your coding skills and familiarize yourself with Streamlit.

In this tutorial, we’ve covered how to set up the Python file, import Streamlit, add a title, and a horizontal line to our calculator app. In the next tutorial, we’ll explore how to add calculator buttons and perform basic calculations.

Keep practicing, and most importantly, have fun!

## Adding User Input and Mathematical Operations

In the previous tutorial, we looked at how to create the basic structure of our calculator app by setting up the Python file, importing the Streamlit library, and adding a title and horizontal line. In this tutorial, we’ll explore how to accept user input, add mathematical operations as radio button options, and perform calculations.

## Importance of Getting User Input for a Calculator App

Building a calculator app requires accepting input from the user. This input is usually numerical values and mathematical operators.

User input enables the calculator app to compute the result of the desired mathematical operation and provide feedback to the user. The user interface design is critical for a calculator app, as it must be straightforward and intuitive to use.

Streamlit’s built-in functions make it easy to build user interfaces that are both intuitive and visually appealing.

## Using numeric_input() to Accept Numerical Values

Streamlit provides a function called `numeric_input()` that allows us to accept numerical values from the user. This function creates a slider or a text box, depending on the input range specified.

Here’s an example code snippet that uses `numeric_input()` to accept numerical values:

```
num1 = st.number_input("Enter the first number")
num2 = st.number_input("Enter the second number")
```

In the code above, we’ve created two numerical input fields that allow the user to enter the first and second numbers, respectively. The `number_input()` function also accepts optional parameters, such as the minimum and maximum input range and the step size.

## Adding Mathematical Operations

Now that we can accept numerical values from the user let’s add mathematical operations to our calculator app. We’ll use radio buttons to add mathematical operations.

Radio buttons allow the user to select one option from a list of choices. Streamlit provides the `radio()` function that creates radio buttons:

`operator = st.radio("Select an operation", ["Addition", "Subtraction", "Multiplication", "Division"])`

In the code above, we’ve created a radio button group with four options: “Addition”, “Subtraction”, “Multiplication”, and “Division”.

The `radio()` function requires two arguments: the question or prompt for the user and the list of options.

## Limitation of Radio Buttons to One Selection at a Time

Radio buttons have a significant limitation, and that is they allow the selection of only one option at a time. We can overcome this limitation by using a drop-down menu or checkbox, depending on the requirements of our calculator app.

Drop-down menus allow us to display a list of options in a dropdown, while checkboxes allow multiple selections. Here’s an example code snippet that uses a drop-down menu:

`operator = st.selectbox("Select an operation", ["Addition", "Subtraction", "Multiplication", "Division"])`

In the code above, we’ve replaced the radio buttons with a dropdown menu.

The `selectbox()` function works similarly to the `radio()` function, with the main difference being that the user can only select one option at a time.

## Performing Calculations

Now that we can accept user input and have added mathematical operations let’s perform calculations. We’ll use an `if-else` statement and basic arithmetic operations to compute the result of the chosen mathematical operation.

Here’s an example code snippet that performs an addition:

```
if operator == "Addition":
result = num1 + num2
st.write("Result: ", result)
```

In the code above, we’ve used an `if` statement to check if the selected operator is “Addition”. If it is, we add the first and second numbers and store the result in a variable called `result`.

Finally, we use the `write()` function to display the result to the user.

## Conclusion

In this tutorial, we’ve covered how to accept user input and add mathematical operations as radio buttons. We’ve also looked at the limitations of radio buttons and how to overcome them using drop-down menus or checkboxes.

Finally, we’ve explored how to perform calculations based on user input and display the result to the user. In the next tutorial, we’ll add more advanced features to our calculator app, such as a scientific calculator functionality.

## Adding Functionality to the Calculator App

In the previous tutorial, we covered adding user input and mathematical operations to our calculator app.

In this tutorial, we’ll explore how to create a function to perform the selected operation, check for division by zero errors, display the result, and add a calculate button to our calculator app.

## Functionality to the Calculator

To perform the selected operation based on user input, we need to create a function that takes in the selected operator and two numerical inputs and returns the result. Here’s an example code snippet that creates a function called `calculate()` that performs the operation based on the selected operator:

```
def calculate(operator, num1, num2):
if operator == "Addition":
result = num1 + num2
elif operator == "Subtraction":
result = num1 - num2
elif operator == "Multiplication":
result = num1 * num2
else:
if num2 == 0:
result = "Cannot divide by zero"
else:
result = num1 / num2
return result
```

In the code above, we’ve created a function that takes in the selected operator, the first number, and the second number as parameters.

The `if-elif` statement checks the operator and performs the corresponding operation. Note that we’ve added an error-checking condition for division by zero errors.

## Checking for Division by Zero Error

In the `calculate()` function above, we’ve added an error-checking condition for division by zero errors. This is essential because dividing by zero is mathematically undefined and can cause errors in our program.

If an error occurs, we display the message “Cannot divide by zero” to the user. We can improve error handling by using Streamlit’s error status element or by providing more detailed error messages.

## Displaying the Result with a Streamlit Success Status Element

Once we’ve computed the result, we need to display it back to the user. We can use Streamlit’s `success()` function to display the result with a success status element:

```
result = calculate(operator, num1, num2)
if isinstance(result, str):
st.error(result)
else:
st.success(f"Result: {result}")
```

In the code above, we’ve assigned the result of the `calculate()` function to a variable called `result`.

If the result is a string, we display an error message using the `error()` function. Otherwise, we display the result with a success status element using the `success()` function.

## Adding the Calculate Button

Now that we’ve created the `calculate()` function and added error handling and result display let’s add a calculate button to our calculator app. The calculate button is essential as it allows the user to explicitly initiate the calculation process.

We can use Streamlit’s `button()` function to create a calculate button that triggers the `calculate()` function:

```
if st.button("Calculate"):
result = calculate(operator, num1, num2)
if isinstance(result, str):
st.error(result)
else:
st.success(f"Result: {result}")
```

In the code above, we’ve wrapped the code that performs the calculation and displays the result in an `if` statement that checks if the “Calculate” button is pressed. If the button is pressed, we compute the result using the `calculate()` function and display the result using the `success()` or `error()` function, depending on the result.

## Conclusion

In this tutorial, we’ve explored adding functionality to our calculator app by creating a `calculate()` function, error-checking for division by zero errors, displaying the result with a Streamlit success status element, and adding a calculate button. We’ve covered the importance of adding a calculate button and tying it to the `calculate()` function.

In the next tutorial, we’ll look at adding more advanced features to our calculator app, such as scientific calculator functionality.

## Example Usage of the Calculator App

In the previous tutorials, we covered various aspects of creating a calculator app in Python using Streamlit. In this tutorial, we’ll give an example of how to use the calculator app to perform basic operations, such as addition, subtraction, multiplication, and division.

Additionally, we’ll explore the division by zero error and how our app handles it.

## Example Usage of the Calculator App

Let’s take a look at how to use our calculator app to perform basic mathematical operations.

### Adding Numbers

- Enter the first number in the “Enter the first number” field.
- Enter the second number in the “Enter the second number” field.
- Select “Addition” in the dropdown menu.
- Click the “Calculate” button.

The app will then display the result of the addition in a success status element.

### Subtracting Numbers

- Enter the first number in the “Enter the first number” field.
- Enter the second number in the “Enter the second number” field.
- Select “Subtraction” in the dropdown menu.
- Click the “Calculate” button.

The app will then display the result of the subtraction in a success status element.

### Multiplying Numbers

- Enter the first number in the “Enter the first number” field.
- Enter the second number in the “Enter the second number” field.
- Select “Multiplication” in the dropdown menu.
- Click the “Calculate” button.

The app will then display the result of the multiplication in a success status element.

### Dividing Numbers

- Enter the first number in the “Enter the first number” field.
- Enter the second number in the “Enter the second number” field.
- Select “Division” in the dropdown menu.
- Click the “Calculate” button.

If the second number entered is not zero, the app will display the result of the division in a success status element. If the second number entered is zero, the app will display an error message stating: “Cannot divide by zero.”

## Conclusion

In conclusion, we’ve successfully created a calculator app using Streamlit and Python. We’ve explored adding basic mathematical operations, creating a `calculate()` function, and error-handling division by zero errors.

Additionally, we’ve shown how to use the calculator app to perform addition, subtraction, multiplication, and division. With the completion of this tutorial, it’s essential to note that our calculator app is highly customizable.

We can add more advanced features, such as a scientific calculator. So, keep exploring, learning, and having fun coding!

## Conclusion

In this tutorial series, we have explored how to create a calculator app using Streamlit in Python.

We’ve covered the importance of practice and building a strong foundation, how to accept user input, add mathematical operations, and display the result using Streamlit’s built-in functions. We’ve also added a calculate button and a function to perform the selected operation and handled the division by zero error.

By creating this program, we’ve learned the importance of user experience design, error handling, and function creation. It’s crucial to keep exploring and learning new concepts in Python, as it’s an essential skill for today’s technological age.