Developer Cheat Sheets

Regex Metacharacters & Syntax

Pattern	Meaning	Example
.	Any character (except newline)	a.c → abc, a1c
\d	Digit [0-9]	\d+ → 123
\w	Word character [a-zA-Z0-9_]	\w+ → hello_world
\s	Whitespace	a\sb → a b
\D	Non-digit	\D+ → abc
\W	Non-word character	\W → !
\S	Non-whitespace	\S+ → hello
^	Start of string/line	^Hello
$	End of string/line	world$
*	Zero or more	ab*c → ac, abc, abbc
+	One or more	ab+c → abc, abbc
?	Zero or one	colou?r → color, colour
{n}	Exactly n times	\d{4} → 2026
{n,m}	Between n and m times	\d{2,4} → 12, 123, 1234
[abc]	Character class	[aeiou] → matches a vowel
[^abc]	Negated class	[^0-9] → non-digits
(a\|b)	Alternation (OR)	(cat\|dog) → cat or dog
()	Capturing group	(\w+)@\1 → repeat capture
(?:)	Non-capturing group	(?:abc)+ → abcabc
(?=)	Positive lookahead	\d(?=px) → 3 in "3px"
(?!)	Negative lookahead	\d(?!px) → 3 in "3em"

Command	Description
git init	Initialize a new repository
git clone	Clone a remote repository
git status	Show working tree status
git add .	Stage all changes
git add -p	Stage changes interactively
git commit -m "msg"	Commit staged changes
git commit --amend	Amend the last commit
git log --oneline	Compact commit history
git diff	Show unstaged changes
git diff --staged	Show staged changes
git branch	Create a new branch
git checkout -b	Create and switch to branch
git merge	Merge branch into current
git rebase	Rebase onto another branch
git push origin	Push to remote
git pull --rebase	Fetch and rebase (cleaner)
git stash	Temporarily shelve changes
git stash pop	Restore shelved changes
git reset --soft HEAD~1	Undo last commit (keep changes staged)
git reset --hard HEAD~1	Undo last commit (discard changes)
git cherry-pick	Apply a specific commit
git reflog	Show all HEAD movements (recovery)

Code	Meaning	Common Use
200	OK	Successful GET, PUT, DELETE
201	Created	Successful POST
204	No Content	Successful DELETE with no body
301	Moved Permanently	Permanent redirect
302	Found	Temporary redirect
304	Not Modified	Cache hit (conditional request)
400	Bad Request	Malformed syntax / validation error
401	Unauthorized	Missing or invalid auth
403	Forbidden	Auth valid but no permission
404	Not Found	Resource doesn't exist
409	Conflict	Duplicate / version conflict
422	Unprocessable Entity	Valid syntax, semantic errors
429	Too Many Requests	Rate limit exceeded
500	Internal Server Error	Uncaught server exception
502	Bad Gateway	Upstream server error
503	Service Unavailable	Server overloaded / maintenance

Code	Description
f"{name=}"	Debug f-string (shows name=value)
if __name__ == "__main__"	Script entry point guard
dict.get(k, default)	Safe key access with fallback
list[::-1]	Reverse a list/string
enumerate(iterable)	Get index + value pairs
zip(a, b)	Iterate two sequences in parallel
{k: v for k, v in items}	Dict comprehension
any() / all()	Short-circuit boolean checks
collections.Counter	Count occurrences
itertools.product	Cartesian product
dataclass	Auto-generate __init__, __repr__, __eq__
pathlib.Path	Modern path handling (replaces os.path)
try/except/else/finally	Complete exception handling
with open(f) as fh	Context manager for file handling
from __future__ import annotations	Delayed annotation eval (3.9+)

Code	Description
const / let	Block-scoped declarations (never use var)
?. (optional chaining)	obj?.prop — safe nested access
?? (nullish coalescing)	value ?? fallback — null/undefined only
`string ${expr}`	Template literals
[...arr]	Spread / shallow copy
{...obj}	Object spread / merge
.map() / .filter() / .reduce()	Array transformations
Object.entries(obj)	Get [key, value] pairs
Object.fromEntries(pairs)	Convert pairs back to object
async / await	Promise-based async code
Promise.allSettled()	Wait for all — no short-circuit
import() (dynamic)	Lazy / conditional module loading
structuredClone(obj)	Deep clone (built-in)
crypto.randomUUID()	Generate UUID v4 (built-in)