Python Cheatsheet

Python list/dict comprehensions, f-strings, file I/O, dataclasses and more

Python Cheatsheet

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📋 List Operations

List comprehension

Filtered list comprehension

Nested comprehension

Apply function to each element

Keep elements where fn returns True

Fold list to single value

Sort by key, descending

Multi-key in-place sort

Pair elements from two lists

Merge two lists

Every other element (step slice)

Reverse list

📖 Dict Operations

Dict comprehension

Filtered dict comprehension

Get with default (no KeyError)

Get or set default value

Merge dicts (d2 wins on conflict)

Merge dicts (Python 3.9+)

Update dict in-place (Python 3.9+)

Remove key, return value (no error if missing)

Build dict from two lists

Sort dict by value

Count occurrences

Dict with default factory

🔤 String Formatting

f-string (Python 3.6+)

f-string with 2 decimal places

Thousands separator

Zero-pad to width 8

Left-align in 20 chars

Use repr() in f-string

Expression in f-string

Join list to string

Trim whitespace

Replace substring

Split with limit

Remove common leading whitespace

📂 File I/O

Read entire file

Read lines as list

Write file (overwrite)

Append to file

Parse / serialize JSON

Read CSV as dicts

Path object (modern)

Read/write with pathlib

Glob files with pathlib

Create directory recursively

⚙️ Functional & Itertools

Flatten/chain iterables

Take first 10 from iterator

Group consecutive elements

Cartesian product

All combinations of size 2

All permutations of size 2

Memoize function results

Partial application

🛡️ Error Handling & Context

Exception handling

Raise exception

Chain exceptions

Suppress specific exception

Create context manager with generator

Assert with message

🏗️ Classes & Dataclasses

Dataclass with default

Immutable dataclass

Key dunder methods

Context manager protocol

Iterator protocol

Property getter/setter

Class and static methods

Mutable default with field()

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