Python: Do This, Not That!

Preface

This book is a compact guide to writing clear, idiomatic Python. Each chapter uses a small example to contrast a clumsy approach with a cleaner one, with an emphasis on readability first and performance second.

The intended audience is Python developers who already know the language basics and want sharper instincts for everyday code review decisions. The examples are deliberately short, but the underlying goal is practical: write code that is easier to read, easier to change, and less error-prone.

Under each major section, you will see two sub-sections: Don't Do This and Do This. Treat them as rules of thumb, not absolute laws. Python is full of tradeoffs, and the “better” choice depends on context. In this edition, the examples target modern Python 3 and favor current best practices over historical Python 2 compatibility.

Ideas and code examples are adapted from [YaK, RaH, JeK] and from the wider Python community.

To follow along, you only need a recent Python 3 installation and a way to run short scripts or a REPL. A virtual environment is recommended.

python3 -m venv .venv
source .venv/bin/activate

You can then paste the snippets into python or save them to small files as you work through the chapters.

The diagram below shows the overall shape of the book: it starts with everyday coding habits, then moves into data and file handling, and finally closes with version-specific patterns from newer Python releases.

That flow mirrors the intent of the book: sharpen judgment on common review comments first, then apply the same “do this, not that” mindset to more specialized and version-dependent features.

The chapters are grouped into core patterns first, followed by patterns that depend on newer Python versions.

Core Patterns

Basics

• 1. Collection initialization
• 2. Chained comparison operators
• 3. Falsy and truthy
• 4. Ternary operator
• 5. Use any and all for boolean scans
• 6. Use is None for None checks
• 7. Use the walrus operator to avoid repeated work in conditions

Loops and Iteration

• 1. Looping over a range of numbers
• 2. Looping backward
• 3. Looping over a collection
• 4. Looping over a collection with indices
• 5. Looping over two collections
• 6. Use enumerate(start=…) for numbered loops
• 7. Use next with a default for searches
• 8. Use deque for queue operations
• 9. Use heapq for top-N selection
• 10. Combinations of a list
• 11. Cycling through a list
• 12. Product of lists

Lists and Comprehensions

• 1. Use list comprehensions
• 2. Filtering a list
• 3. Count matching items without a temporary list
• 4. Most frequent item in list
• 5. Dictionary comprehension
• 6. Set comprehension

Tuples and Strings

• 1. Unpacking sequences and tuples
• 2. Ignoring unpacked values from a tuple
• 3. Avoid accessing tuple elements by index
• 4. String concatenation
• 5. String interpolation
• 6. String debug
• 7. Don’t repeat yourself (DRY)
• 8. String reversal
• 9. Use removeprefix and removesuffix

Functions and Context

• 1. Clarify function calls with keyword arguments
• 2. Lambdas
• 3. Generator functions
• 4. Use contextlib.suppress for narrow ignored exceptions
• 5. Use nullcontext for optional context managers

Dictionaries and Data

• 1. Default dictionary values: defaultdict
• 2. Accessing a dictionary value with a default value
• 3. Updating dictionaries
• 4. Merging dictionaries
• 5. Using a dictionary to store counts
• 6. Transforming data with map, filter, reduce
• 7. Flattening data
• 8. Caching data and results

Files, Paths, and Exceptions

• 1. Reading a file
• 2. Deleting a file
• 3. Filtering files
• 4. Saving objects to file
• 5. Prefer pathlib over os.path
• 6. Re-raise exceptions deliberately

Classes and Misc

• 1. Classes and dunders (double underscores)
• 2. Enumerations
• 3. Use default_factory for mutable dataclass defaults
• 4. Simultaneous state updates
• 5. Pandas apply and numpy vectorization

Version-Specific Patterns

General Modern Python

• 1. New vs old classes
• 2. Use explicit namespaces with exec and eval

Python 3.9+

• 1. Use functools.cache for unbounded memoization

Python 3.10+

• 1. Use zip(strict=True) when equal lengths are required
• 2. Use dataclass(slots=True) for simple records
• 3. Use structural pattern matching for structural dispatch

Python 3.11+

• 1. Use StrEnum for string enums
• 2. Use Self for fluent instance return types
• 3. Use tomllib for reading TOML
• 4. Use asyncio.TaskGroup for related tasks
• 5. Use add_note for extra exception context
• 6. Use except* for exception groups

Python 3.12+

• 1. Use Path.walk in pathlib code
• 2. Use explicit case sensitivity in pathlib globbing
• 3. Use the type statement for type aliases
• 4. Use @override for overridden methods
• 5. Use itertools.batched for chunking

Python 3.13+

• 1. Use copy.replace for shallow field updates
• 2. Use Queue.shutdown instead of sentinel values

Python 3.14+

• 1. Use InterpreterPoolExecutor for isolated parallel workers
• 2. Use concurrent.interpreters instead of custom wrappers
• 3. Use compression.zstd for standard-library Zstandard
• 4. Use template strings for structured interpolation

About

One-Off Coder is an educational, service and product company. Please visit us online to discover how we may help you achieve life-long success in your personal coding career or with your company’s business goals and objectives.

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Copyright

This work is licensed under a Creative Commons Attribution 4.0 International License by One-Off Coder.



The full source code is available on GitHub.

Cite this book as follows.:

@misc{oneoffcoder_python_dothis_2019,
title={Python: Do This, Not That!},
url={https://python.oneoffcoder.com},
author={One-Off Coder},
year={2019},
month={Oct}}

Bibliography

[YaK]

Intermediate python. https://book.pythontips.com/en/latest/index.html. Accessed: 2019-10-18.

[RaH]

Transforming code into beautiful, idiomatic python. https://www.youtube.com/watch?v=OSGv2VnC0go. Accessed: 2019-10-18.

[JeK]

Writing idiomatic python. https://jeffknupp.com/writing-idiomatic-python-ebook/. Accessed: 2019-10-18.

Author

Jee Vang, Ph.D.

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