What are Functions?

• Functions are self-contained, reusable blocks of code that perform a specific task.
• They take an input, perform a task on that input (such as a calculation or transformation), and return a result.
• Functions help to organise code, avoid repetition, and make complex processes easier to understand and maintain.

Anatomy of a Function

• Understanding how to use (and create) functions can feel a little abstract at first.
• Functions must have names (how they are called), arguments (inputs passed to it), statements (the tasks carried out), and return values (the output/result it returns).
• Python functions are structured as below:

Shop-Bought Versus Home-Baked

• All languages come with built-in functions available - you will have used some of Python’s built-in functions already, for example print(), type() and sum().
• They operate exactly the same as ones you make yourself - they are called, they take an argument and they return a result.
• You can create your own functions or use pre-built functions either provided by the language itself or by others (imported from packages/libraries).

Functions Are Not New

• While functions are a fundamental building block of programming, they exist anywhere that you might write code.
• For example, Excel includes lots of functions (for example, SUM(), VLOOKUP(), LINEST()), as does SQL ( for example, COUNT(), AVG(), COALESCE())!
• Functions work very similarly in whatever language you might use, i.e. they have the same component parts. What changes is the syntax.

Advantages of Functions

• Reusability - Write code once and use it multiple times. Stay DRY (Don’t Repeat Yourself)!
• Modularity - Break down complex tasks into smaller, manageable chunks.
• Readability - Make code clearer and more organised.
• Maintainability - Easier to make changes to one part of the code without breaking everything.
• Reliability - More efficient code with fewer errors that others can follow.

Best Practices

• Use Descriptive Names - Give your function a name that describes what it does.
• Perform One Task - Functions should carry out a single task so as to avoid unnecessary complexity.
• Document Your Functions - There are lots of ways to help anyone using your functions (including future you), such as docstrings and type hints.
• Avoid Side Effects - Functions should not change anything outside of itself.
• Explicitly Handle Errors - Setting guardrails helps avoid unexpected consequences.
• Write Testable Code - Functions should be easy to test (and should be tested).

What are Programming Paradigms

• Programming paradigms are just the different approaches or styles to programming that define how code is structured/organised.
• Functional and Object-Oriented Programming (OOP) are two of the most common paradigms.
• Languages like Java, C++, and Ruby are OOP, while languages like Haskell and Scala are functional.
• Lots of languages (including Python) can support multiple paradigms.

What is Functional Programming?

Functional programming is a programming paradigm — a style of building the structure and elements of computer programs — that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data.

What is Functional Programming, Actually?

• In simple (and perhaps not entirely accurate) terms, functional programming just focuses on the use of functions for writing code.
• Functional programming treats coding as the evaluation of mathematical functions and avoids changes in state or mutable data.
• It relies on “pure” functions that always produce the same output for the same inputs, and do not cause side effects!

Conclusion

• Functions are a great way to organise and simplify your code, and avoids repetition and inefficiency.
• Understanding how functions work is key to learning to use them, create them, and debug them.
• Understanding functional programming is key to following along in conversations with nerds.