Week 1 - Python Foundations

Python Setup

Data Types and Variables

Control Flow: Logic and Loops

Functions and Modules

Type Hints for Clearer Code

Command-Line Interface Habits

Errors and Debugging

Logging in Python

File Operations

Azure Setup and Account Access

Practice

Week 1 Gotchas & Pitfalls

Week 1 Assignment: The Data Cleaning Pipeline

Week 1 Glossary

Going Further: Optional Deep Dives

Week 1 Kickoff Slides

Functions and Modules

Organizing code into functions and modules is essential for building maintainable data pipelines.

Functions Review

You learned functions in Core. Here's what's important for data engineering:

def clean_value(value: str, default: str = "") -> str:
    """Clean and normalize a string value.

    Args:
        value: The string to clean
        default: Value to return if input is empty

    Returns:
        Cleaned string, lowercase and stripped
    """
    if not value:
        return default
    return value.strip().lower()

<aside> 💡 Always write docstrings. They help your future self and teammates.

</aside>

Modules

A module is simply a .py file. You can import functions from it.

# `utils.py`
def clean_value(value):
    return value.strip().lower()

# `main.py`
from utils import clean_value
print(clean_value("  HELLO  "))

The __name__ == "__main__" Pattern

This pattern lets a file work both as a module AND as a script:

# `utils.py`
def clean_value(value):
    return value.strip().lower()

if __name__ == "__main__":
    # Only runs when executed directly
    print(clean_value("  TEST  "))

<aside> ⌨️ Hands on: Create utils.py with a function, import it in main.py.

</aside>

<aside> 🚀 Try it in the widget: https://lasse.be/simple-hyf-teach-widget/?week=1&chapter=functions_and_modules&exercise=modules_demo&lang=python

</aside>

🧠 Knowledge Check

• 1. What is the purpose of a docstring, and what command in a Python REPL prints one?
• 2. What does the if __name__ == "__main__": block allow a single file to do, and what is __name__ set to when the file is imported?
• 3. If you have a file named utils.py with a function clean(), give two different ways to import and use it from main.py. When would you reach for each?
• 4. Why is using a mutable default argument value (e.g., def add_record(records=[]):) a footgun?
• 5. A teammate writes a 300-line script that does extract, transform, and load all in one file. What would you suggest they split into separate modules, and why?

Extra reading

Articles

• Variables in Python: Usage and Best Practices — Comprehensive guide covering creation, naming, and dynamic typing.
• Basic Data Types in Python — Deep dive into integers, floats, strings, and booleans.
• Python Dictionaries In Depth — Essential for understanding key-value data structures.

Videos

• Python Tutorial for Beginners 2 - Strings — Corey Schafer's clear explanation of string operations (22 min).
• Python Tutorial for Beginners 4 - Lists, Tuples, and Sets — Practical examples of Python collections (29 min).

Next lesson: Type Hints

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