Python Cheat Sheet: Your Go‑To Quick Reference

Ever feel stuck staring at a blank screen, wondering how to write that list comprehension or slice a string? A solid cheat sheet can turn those moments into "aha!" seconds. Below you’ll find the most useful one‑liners, built‑in functions, and library shortcuts you’ll actually use day‑to‑day.

Core Syntax & One‑Liners

Start with the basics you need to type less and think more. len() tells you the size of any iterable, enumerate() gives you index/value pairs without a manual counter, and zip() merges two lists in a single line. Need a quick filter? [x for x in seq if condition] replaces verbose loops, and {k: v for k, v in dict.items() if v} cleans up dictionaries on the fly.

String tricks are often the hidden gems. "-".join(map(str, my_list)) creates a delimited string, while f"{var:.2f}" formats numbers to two decimals in an f‑string. Slice any list with my_list[start:stop:step] – it works for strings, tuples, and even NumPy arrays.

Data Structures & Handy Libraries

When you need a stack or queue, use list.append() and list.pop() for LIFO, or collections.deque for O(1) FIFO operations. Want a default value for missing keys? defaultdict(lambda: 0) saves you a bunch of if key in dict checks.

Most Python projects lean on a few core libraries. requests.get(url).json() pulls JSON data in one line. pandas.read_csv('file.csv') loads tabular data instantly, and matplotlib.pyplot.plot(x, y) draws quick graphs. Remember to import only what you need – from datetime import datetime as dt makes timestamps clearer.

Debugging doesn’t have to be a nightmare. Drop import pdb; pdb.set_trace() anywhere to pause execution and inspect variables. Or use the built‑in print() with f‑strings for quick checks: print(f"value: {val}"). For larger apps, the logging module gives you timestamps, levels, and file output without cluttering your code.

Putting the cheat sheet to work is simple: keep a markdown file or a printable PDF on your desk, and scan it before you start a new script. The more you reference it, the faster those patterns become second nature. Over time you’ll replace whole blocks of code with neat one‑liners, and your code will read cleaner.

Remember, a cheat sheet isn’t a crutch; it’s a shortcut to reinforce what you already know. Use it to fill gaps, experiment with new functions, and discover alternatives you didn’t realize existed. Happy coding!