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L4: Function Fundamentals
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Overview
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This lecture introduces Python functions as the primary tool for organizing code into reusable, modular units. You will learn how to define and call functions, work with different argument types, understand Python's scope rules (LEGB), explore pass-by-assignment behavior, add type hints for clarity, write Google-style docstrings, and use recursion to solve problems that have a recursive structure.


.. admonition:: Learning Objectives
   :class: learning-objectives

   By the end of this lecture, you will be able to:

   - Define and call functions using the ``def`` keyword with parameters and return values.
   - Distinguish between positional, default, keyword, ``*args``, and ``**kwargs`` arguments.
   - Explain the LEGB scope rule and predict how Python resolves variable names.
   - Describe how pass-by-assignment works with mutable and immutable objects.
   - Annotate functions with type hints including ``Optional``, ``Union``, and Python 3.10+ pipe syntax.
   - Write Google-style docstrings with descriptions, ``Args``, and ``Returns`` sections.
   - Implement recursive functions with proper base cases and recursive cases.


.. toctree::
   :maxdepth: 2
   :titlesonly:
   :hidden:

   l4_lecture
   l4_exercises
   l4_quiz
   l4_references

Next Steps
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- In the next lecture, we will cover Advanced Functions:

  - Programming paradigms (procedural, functional, OOP)
  - First-class functions and lambdas
  - Closures and callables
  - Decorators
  - Partial functions

- Review and experiment with all code snippets and exercises from today's lecture.
- Practice writing functions with different argument types and type hints.
- Read `Python Official Tutorial <https://docs.python.org/3/tutorial/>`_ -- Section 4.7 (Defining Functions).