Calculating the change in percentage between two numbers is a common task in Python. There are several ways to solve this problem, each with its own advantages and disadvantages. In this article, we will explore three different approaches to calculate the change in percentage between two numbers in Python.

## Approach 1: Using the Formula

The simplest way to calculate the change in percentage between two numbers is by using the formula:

`percentage_change = ((new_number - old_number) / old_number) * 100`

Let’s see an example:

```
old_number = 50
new_number = 75
percentage_change = ((new_number - old_number) / old_number) * 100
print(f"The percentage change is: {percentage_change}%")
```

This will output:

`The percentage change is: 50.0%`

This approach is straightforward and easy to understand. However, it may result in a ZeroDivisionError if the old_number is zero. To avoid this, we can add a check to handle this edge case.

## Approach 2: Using a Function

Another way to calculate the change in percentage is by defining a function that takes the old and new numbers as arguments:

```
def calculate_percentage_change(old_number, new_number):
if old_number == 0:
return "Cannot calculate percentage change when the old number is zero."
percentage_change = ((new_number - old_number) / old_number) * 100
return percentage_change
old_number = 50
new_number = 75
percentage_change = calculate_percentage_change(old_number, new_number)
print(f"The percentage change is: {percentage_change}%")
```

This will output the same result as before:

`The percentage change is: 50.0%`

Using a function allows us to handle the edge case of a zero old_number more gracefully. It also makes the code more reusable, as we can easily calculate the percentage change for different pairs of numbers.

## Approach 3: Using the Decimal Module

When dealing with financial calculations or situations where precision is crucial, it is recommended to use the Decimal module in Python. This module provides support for decimal floating-point arithmetic.

Here’s an example of calculating the percentage change using the Decimal module:

```
from decimal import Decimal
old_number = Decimal('50')
new_number = Decimal('75')
percentage_change = ((new_number - old_number) / old_number) * 100
print(f"The percentage change is: {percentage_change}%")
```

This will output the same result as before:

`The percentage change is: 50.0%`

Using the Decimal module ensures that the calculations are performed with the desired precision, avoiding any potential rounding errors that may occur with regular floating-point arithmetic.

After exploring these three approaches, it is clear that the best option depends on the specific requirements of your project. If precision is crucial, using the Decimal module is recommended. Otherwise, the first approach using the formula or the second approach using a function are both valid choices.