Software Refactoring: How to Keep Your Code Clean & Scalable

In software development, it’s common for code to not always be implemented optimally — whether due to time pressure, unclear requirements, or the continuous evolution of features. These factors can lead to problems like bugs and excessive complexity, which affect the software’s maintenance and evolution.

That’s where refactoring comes in.

Refactoring is an essential practice for addressing these issues. It improves code readability, maintainability, and efficiency without changing functional behavior. 

In this article

Here we’ll cover how to spot signs that your code needs refactoring, like code smells. You’ll learn the best way to refactor efficiently while reducing the risk of new bugs. Plus, we’ll walk through a practical example and show how principles like KISS, DRY, and SOLID help keep your code clean and maintainable for the long run.

• Definition of code refactoring
• Identifying issues in code
• Identifying code smells
• The refactoring process
• Refactoring example in action

What is refactoring in software development?

Refactoring – or code refactoring – is the process of restructuring existing code to improve its readability, efficiency, and maintainability — all without changing its external behavior. 

It’s a bit like cleaning and reorganizing your desk to make it easier to find and use all your pens, notepads, gadgets, and more. The desk is still where you get work done. It’s just been slightly rearranged to make things more manageable. 

Whether you’re reducing code duplication, simplifying complex functions, or reorganizing modules, refactoring improves the structure of your codebase, ensuring that it evolves with the needs of your project. 

Identifying issues in code

Let’s clarify something important: The need for refactoring is not necessarily linked to the quality of the code itself. Any software in constant maintenance will inevitably require periodic reorganization, no matter how skilled the team is. 

There are various reasons to reorganize code that is running just fine, including: 

• Lack of clarity
• Preparing the code for future features
• Changing a module’s design pattern due to new external integrations
• Updating language versions, frameworks, or dependencies, or addressing the need for new features or security vulnerabilities.

As software scales, refactoring can also become necessary. For example, queries may need to be refactored, functions might need to be organized to be more testable, and tests might need to be added for high availability and load handling. 

So, as software evolves and attracts more users, optimizations become inevitable. As Martin Fowler recommends in Refactoring, refactoring should be a step before optimization.

When we stop the development of new features and bug fixes to refactor part of the code, we need to remember that, like any other change, this process can introduce bugs, which will require development time to fix. 

For this reason, you need to carefully evaluate code reorganization, considering several important factors, including:

• Type of project: Refactoring is most beneficial for classes, files, and modules that are constantly maintained. However, making large-scale reorganizations to long-standing code with no foreseeable updates can be risky. Therefore, these changes need a thorough evaluation.
• Project stage: It’s important to understand the project’s current needs. Is your focus on rapid feature delivery or bug fixes to stabilize a version? Or is the software already stable, and you have time to refactor and implement new features?
• Refactor size: Based on the previous points, the flexibility of day-to-day operations can influence the size of the refactor. Depending on the change’s scope, refactoring might still be possible even with limited time and legacy code. However, very large-scale refactors may not be advisable, even when there’s some time allocated for development.

To assess the need and scale of refactoring, you need to look for “code smells,” which are indicators of potential issues in the code that could lead to problems in the future or areas that need improvement. 

Identifying code smells

Before you refactor, you need to root out any potential issues you might encounter. Here are key code smells you need to watch for in the code and the software’s evolution plan and how to identify them.

Variable naming

Variables should have names that clearly describe the value they hold. Ambiguous or overly generic names can make the code difficult to understand.

Long functions and methods

Long functions or methods may indicate an accumulation of responsibilities. In these cases, it’s necessary to break down the functionality into smaller, more focused functions.

Code duplication

Identical code blocks appearing in multiple places within the project suggest the need to extract that code into a reusable function or method.

Excessive conditionals

When a class has methods with numerous if or switch statements, it may indicate the need to split the class responsibilities or use polymorphism to create specific methods for each conditional case.

Excessive use of primitive types

This is a subtler issue, often noticeable when you’re familiar with the code. You might find many related variables (such as a group of integers or strings) that could be better represented as a more complex data type, like a list, dictionary, or class. This would make the code cleaner and easier to read.

Global variables

Using global variables that are not constants and are accessed by multiple functions is risky. Tracking their values can become complicated, leading to potential bugs. The goal should be to pass values as parameters, making the function more predictable, pure, and easier to test.

Issues found in maintenance

In addition to these easily identifiable smells, some issues only emerge during maintenance, suggesting the need for a more significant refactoring, including:

• Feature envy: Methods that rely more on data from other classes than their own. This indicates the need to reconsider the responsibilities of the classes or reorganize the data into new classes.
• Shotgun surgery: When a small change requires modifying code in multiple locations across the project. This may suggest that functionalities or data should be grouped more effectively.
• Use of external libraries for simple tasks: When third-party libraries are used for relatively simple tasks, it’s essential to assess whether the complexity of the library justifies the risk of security vulnerabilities, lack of updates, or maintenance issues. 

If the library is not widely known and the implementation is relatively simple, it might be better to implement the functionality internally or even fork the library. 

When using third-party dependencies, evaluate their relevance by examining their GitHub stars, community engagement, and documentation quality.

Choosing parameters carefully in asynchronous tasks: In asynchronous tasks, avoid passing query results as parameters — especially those involving I/O operations. Instead, pass conditional values as parameters and perform the query inside the task itself.

The refactoring process

Now that you know what to look for, it’s time to refactor. Refactoring must be conducted carefully and with a plan to ensure that the changes you introduce minimize the creation of new problems and maintain the system’s stability. 

Ensure test coverage

One of the first essential steps before starting the refactor is ensuring sufficient test coverage. If the code being refactored lacks adequate tests, it’s crucial to write new tests before making any modifications. This enables changes to be validated effectively, reducing the risk of introducing new bugs.

Work in blocks

A recommended approach is to gradually implement changes by refactoring small blocks of code. This makes it easier to spot potential issues and allows for incremental testing of the refactored code, ensuring it continues functioning as expected. 

Key refactoring principles

When refactoring, adhering to key development principles is critical to keep the code clean and organized. The KISS (Keep It Simple, Stupid) principle promotes creating simple and direct solutions, avoiding unnecessary complexity. The DRY (Don’t Repeat Yourself) principle advises eliminating code duplication, making maintenance easier, and reducing errors. 

Additionally, applying SOLID principles ensures the code remains modular, easy to understand, and ready for future extensions.

Use design patterns and linters

Another important aspect of refactoring is using design patterns and linters. Design patterns provide reusable solutions to common problems in software development and help structure code efficiently. 

Linters (programs that perform static analysis on your code), on the other hand, enforce consistent coding practices and flag potential issues, such as style violations or best practice inconsistencies. This promotes uniformity, which enhances the code’s maintainability and readability.

Evaluate the impact on implementation

It’s also essential to evaluate the impact of refactoring on implementation time and complexity. Projects in constant evolution may require frequent changes, which should be handled carefully. 

Large-scale refactors, especially those affecting critical system components, require thorough analysis to prevent instabilities. Therefore, refactoring should always be guided by a clear plan aligned with project priorities to improve long-term maintainability and evolution.

Don’t stop at one refactor

Finally, it’s important to remember that refactoring is not a one-time task. 

It is part of an ongoing software maintenance cycle, helping to prevent code degradation and ensuring that the codebase remains clean, efficient, and capable of meeting future demands.

Continuous refactoring helps avoid the accumulation of technical debt, which can make software maintenance increasingly difficult over time.

Research has shown that regular refactoring can significantly reduce issues related to legacy code, preventing it from becoming a burden on the development team. 

Plus, well-executed refactoring improves code efficiency and facilitates evolution without compromising critical aspects of the software.

Refactoring example in action

Now, it’s time to look at an example of refactoring. Below, we will analyze and refactor a simple order management code by applying best software design practices. 

The original code works well, but several issues could make it harder to maintain, expand, and read as the system grows.

Original code 

In the original code, the Order class handles multiple responsibilities:

• Managing the items in the order.
• Calculating the order total.
• Applying discounts.
• Applying taxes.
• Printing the order details.

These multiple responsibilities in a single class make the code harder to maintain, understand, and extend. Additionally, the use of a tuple to represent each order item (name, quantity, and unit price) makes the code less readable and prone to errors.

Class Order:
    def __init__(self, customer_name, items):
        self.customer_name = customer_name
        self.items = items
        self.price  = 0
        self.discount = 0

    def calculate_total(self):
        total = 0
        for _, quantity, unit_price in self.items:
            total += quantity * unit_price
        self.price = total
        return total

    def apply_discount(self, discount_code):
        if discount_code == 'DISCOUNT10':
            self.discount = 0.1
        elif discount_code == 'DISCOUNT20':
            self.discount = 0.2
        elif discount_code == 'DISCOUNT30':
            self.discount = 0.3
        else:
            self.discount = 0
        self.price -= self.price * self.discount

    def add_item(self, item, quantity, unit_price):
        self.items.append((item, quantity, unit_price))
        self.calculate_total()

    def remove_item(self, item):
        self.items = [i for i in self.items if i[0] != item]
        self.calculate_total()

    def apply_tax(self):
        self.price += self.price * 0.05

    def print_order(self):
        print(f'Customer: {self.customer_name}')
        for item, quantity, unit_price in self.items:
            print(f'{item} - {quantity} x ${unit_price:.2f}: {(quantity * unit_price):.2f}')
        print(f'Subtotal: ${self.price:.2f}')
        if self.discount > 0:
            print(f'Discount applied: {self.discount * 100:.0f}%')
        self.apply_tax()
        print(f'Total with tax: ${self.price:.2f}')
        print('-' * 30)Code language: Python (python)

Identifying issues in the original code 

1. Excessive responsibilities in the Order class: The Order class manages too many responsibilities. It:
   • Handles items in the order
   • Calculates totals
   • Applies discounts and taxes
   • Print the order details

This makes the class difficult to maintain and extend.

2. Using tuples for items: The code uses tuples to represent order items (name, quantity, and unit price). This is not very readable, which makes it harder to understand the meaning of the data as the code grows.
3. Conditionals for discounts: The apply_discount method uses multiple if/elif conditions to apply discounts. This approach is prone to errors and hard to extend as more discounts are added.
4. Calculating taxes in the print_order method: The logic for applying taxes is embedded in the print_order method, which violates the “separation of concerns” principle.

Proposed refactoring

We will refactor the code to improve readability, separation of concerns, and flexibility:

1. Create a ProductCart class: The responsibility of managing individual items in the order will be extracted to a ProductCart class. This will make the code more readable and encapsulate the details of each product.
2. Use a dictionary for discounts: We will replace the if/elif chain for applying discounts with a dictionary. This will simplify the code and make it easier to add new discount types.
3. Separate calculations from printing: We will refactor the logic for tax and discount calculations into separate methods so that the print_order method only handles printing the order summary.

Refactored code

from typing import List
class ProductCart:
    def __init__(self, name: str, quantity: int, price: float, has_special_discount: bool = False):
        self.name = name
        self.price = price
        self.quantity = quantity
        self.has_special_discount = has_special_discount
        self.total_price = self._special_discount() if has_special_discount else self.calculate_total()

    def calculate_total(self) -> float:
        return self.price * self.quantity

    def _special_discount(self) -> float:
        if self.quantity > 3 and self.has_special_discount:
            return self.calculate_total() - self.price
        return self.calculate_total()

    def print_product(self) -> None:
        print(f'{self.name} - {self.quantity} x ${self.price:.2f}: {self.calculate_total():.2f}')
        if self.has_special_discount:
            print(f'** Special discount applied!')

class Order:
    TAX_RATE = 0.05

    def __init__(self, customer_name: str):
        self.customer_name = customer_name
        self.items: List[ProductCart] = []
        self.discount = 0

    def calculate_total(self) -> float:
        return sum(item.total_price for item in self.items)

    def apply_discount(self, discount_code: str) -> None:
        self.discount = self.get_discount_rate(discount_code)

    def get_discount_rate(self, discount_code: str) -> float:
        discount_rates = {
            'DISCOUNT10': 0.1,
            'DISCOUNT20': 0.2,
            'DISCOUNT30': 0.3
        }
        return discount_rates.get(discount_code, 0)

    def add_item(self, item: ProductCart) -> None:
        self.items.append(item)

    def remove_item(self, item_name: str) -> None:
        self.items = [i for i in self.items if i.name != item_name]

    def calculate_final_total(self) -> float:
        subtotal = self.calculate_total()
        discounted_total = subtotal - (subtotal * self.discount)
        final_total = discounted_total + (discounted_total * Order.TAX_RATE)
        return final_total

    def print_order(self) -> None:
        print(f'Customer: {self.customer_name}')
        for item in self.items:
            item.print_product()

        subtotal = self.calculate_total()
        print(f'Subtotal: ${subtotal:.2f}')
        if self.discount > 0:
            print(f'Discount applied: {self.discount * 100:.0f}%')

        final_total = self.calculate_final_total()
        print(f'Total with tax: ${final_total:.2f}')
        print('-' * 30)

def main():
    order = Order('John Doe')
    order.add_item(ProductCart('apple', 4, 0.5, True))
    order.add_item(ProductCart('banana', 6, 0.3))
    order.add_item(ProductCart('orange', 3, 0.7))
    order.apply_discount('DISCOUNT20')
    order.add_item(ProductCart('pear', 2, 0.8))
    order.remove_item('banana')
    order.print_order()

if __name__ == "__main__":
    main()Code language: Python (python)

Test cases for the refactored code

The test cases remain similar, but we now use the new ProductCart class and the updated Order class. This makes the tests more intuitive and straightforward.

import pytest
from sample_refactored import Order, ProductCart  

@pytest.fixture
def sample_order():
    order = Order('John Doe')
    order.add_item(ProductCart('apple', 4, 0.5))
    order.add_item(ProductCart('banana', 6, 0.3))
    order.add_item(ProductCart('orange', 3, 0.7))
    return order

def test_calculate_total(sample_order):
    total = sample_order.calculate_final_total()
    assert round(total, 2) == 6.19

def test_apply_discount(sample_order):
    sample_order.apply_discount('DISCOUNT20')
    total = sample_order.calculate_final_total()
    assert round(total, 2) == 4.96

def test_add_item(sample_order):
    sample_order.add_item(ProductCart('pear', 2, 0.8))
    total = sample_order.calculate_final_total()
    assert round(total, 2) == 7.88

def test_remove_item(sample_order):
    sample_order.remove_item('banana')
    total = sample_order.calculate_final_total()
    assert round(total, 2) == 4.3Code language: Python (python)

Refactoring is an essential practice in software development because it improves readability, reduces complexity, and facilitates maintenance. 

Although it varies in scale — from small adjustments to major changes — refactoring must be carefully planned and tested to avoid introducing new issues. We can create clearer and more sustainable code by applying principles like KISS, DRY, and SOLID. 

Refactoring is not just about fixing existing code but also about preventing future problems and ensuring that the software continues to evolve healthily.

Learn more about development best practices

Refactoring is just one piece of the puzzle when it comes to creating resilient, scalable, and efficient software. If you’re ready to learn more about software development best practices, check out the rest of the Cheesecake Labs blog. We’ve got lots of expert insights, practical tips, and in-depth guides to help your team build better software. 

Need help with your next software project? At Cheesecake Labs, our software experts specialize in creating clean, scalable, and maintainable solutions tailored to your needs. Send us a message, and let’s chat about bringing your vision to life!