Python Data Types & Strings Cheat Sheet: str Methods, f-strings & Slicing

Python strings are immutable Unicode sequences. Slice with s[start:stop:step], build with f-strings, and split/join for CSV-like data. None, 0, "", and [] are falsy. Distinguish str (text) from bytes (raw) — decode with an explicit encoding, usually UTF-8.

This Python cheat sheet is written for people searching for a fast, accurate reference: students, junior developers, and teams shipping production software. Pin it, copy the snippets, and come back when syntax slips.

Quick reference

• Slice: s[0:3], s[-1], s[::-1] reverse. End index is exclusive.
• split/join: s.split(",") and ",".join(parts) — join needs strings.
• strip: strip, lstrip, rstrip for whitespace or given chars.
• find: in, startswith, endswith, s.find (-1 if missing) or index (throws).
• replace: s.replace("a", "b") returns a new string. Count is optional.
• f-string: f"{price:.2f}", f"{name:>10}" alignment.
• bytes: b"abc", s.encode("utf-8"), b.decode("utf-8").
• bool: bool("") is False. Do not use or for 0 if zero is valid — use is None.

Copy-paste examples

Slug, initials, and money format

f-strings are the default in new code. Avoid % formatting unless matching an old codebase.

def slugify(title: str) -> str:
    keep = []
    for ch in title.strip().lower():
        if ch.isalnum():
            keep.append(ch)
        elif ch.isspace() or ch in '-_':
            keep.append('-')
    return ''.join(keep).strip('-')

def initials(name: str) -> str:
    parts = [p[0] for p in name.split() if p]
    return ''.join(parts).upper()

def money(n: float) -> str:
    return f'${n:,.2f}'

Common mistakes

• Treating user input as bytes and concatenating to str (TypeError).
• is to compare strings (s is "hi") instead of ==.
• Using %s interpolation with untrusted data in SQL — that is not parameterization.
• Assuming len(s) is the number of graphemes for emoji-heavy text.

FAQ

1. str vs repr? str is readable. repr is unambiguous for debugging. f-strings use str unless you use !r.

1. Why is BLOGPH0 returning BLOGPH1? or returns the first truthy value. Zero is falsy. Use an explicit None check for numbers.

1. Multiline strings? Triple quotes """...""". Watch accidental indent in the string body.

Related Python cheat sheets

• Python Cheat Sheet 2026
• Python Lists Dictionaries Cheat Sheet
• Python Functions Oop Cheat Sheet

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