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Don't Repeat Yourself (DRY) in Python 2026 – Best Practices for Writing Functions

The DRY principle — "Don't Repeat Yourself" — is one of the most important concepts in software engineering. In 2026, applying DRY effectively when writing functions leads to cleaner, more maintainable, and less error-prone code.

TL;DR — Key Takeaways 2026

Avoid duplicating logic across functions
Extract repeated code into reusable helper functions
Use parameterization instead of copy-pasting similar functions
Leverage higher-order functions and decorators
Balance DRY with readability — don't over-abstract

1. Common DRY Violation


# ❌ Repeating logic
def calculate_user_score_v1(user):
    score = 0
    score += user.wins * 10
    score += user.level * 5
    score += len(user.achievements) * 3
    return score

def calculate_user_score_v2(user):
    score = 0
    score += user.wins * 10
    score += user.level * 5
    score += len(user.achievements) * 3
    return score

2. Applying DRY Principle


# ✅ DRY version
def _calculate_base_score(user):
    """Private helper to avoid repetition."""
    return (
        user.wins * 10 +
        user.level * 5 +
        len(user.achievements) * 3
    )

def calculate_user_score_v1(user):
    return _calculate_base_score(user) + user.bonus

def calculate_user_score_v2(user):
    return _calculate_base_score(user) + user.special_multiplier

3. Advanced DRY Techniques


# Using higher-order functions
def create_score_calculator(base_multiplier: int):
    def calculate_score(user):
        return (
            user.wins * base_multiplier +
            user.level * 5 +
            len(user.achievements) * 3
        )
    return calculate_score

calc_v1 = create_score_calculator(10)
calc_v2 = create_score_calculator(15)

4. Best Practices for DRY in 2026

Extract repeated logic into small, well-named helper functions
Use parameterization instead of duplicating similar functions
Consider decorators for cross-cutting concerns
Balance DRY with readability — avoid excessive abstraction
Write clear docstrings for helper functions

Conclusion

The DRY principle helps reduce bugs, improve maintainability, and make your codebase easier to understand. In 2026, applying DRY thoughtfully when writing functions is a hallmark of professional Python development.

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