$devvkit resources --cheatsheet python-cheatsheet

Python Cheatsheet

[programming]

Modern Python — data types, control flow, comprehensions, functions, modules, and file I/O.

Python is the go-to language for data science, automation, backend development, and scripting. This cheatsheet covers Python 3.11+ syntax including data structures, comprehensions, f-strings, type hints, and context managers.

All examples assume Python 3.10+ with modern typing support.

Data Types & Structures

$x = 42 # int

Python is dynamically typed. Variables are assigned without type declarations.Example: name: str = "Alice" # Optional type hint

$my_list = [1, 2, 3]

A list is an ordered, mutable collection. Supports mixed types.Example: items = [1, "hello", 3.14]

$my_dict = {"key": "value"}

A dict stores key-value pairs. Keys must be hashable (strings, numbers, tuples).Example: user = {"name": "Alice", "age": 30}

$my_set = {1, 2, 3}

A set is an unordered collection of unique elements. Great for membership tests.Example: unique_ids = {101, 102, 103}

$from typing import Optional

Type hints for better IDE support and static analysis. No runtime effect.Example: def greet(name: str) -> str: return f"Hello {name}"

$class MyClass:

Define a class. Modern Python uses __init__ for constructor.Example: class User: def __init__(self, name): self.name = name

$@dataclass

Auto-generate __init__, __repr__, __eq__ for data-holding classes.Example: @dataclass class Point: x: float y: float

Strings & f-strings

$f"Hello {name}, age {age}"

f-strings — embed expressions in string literals with {}.Example: f"User {user['name']} is {user['age']} years old"

$" ".join(["a", "b", "c"])

Join a list of strings into a single string with a separator.Example: ", ".join(["red", "green", "blue"])

$"hello world".split()

Split a string on whitespace (default) or a delimiter.Example: "a,b,c".split(",")

Control Flow & Loops

$if/elif/else

Conditional branching with elif (not else if or elsif).Example: if x > 0: print("positive") elif x == 0: print("zero") else: print("negative")

$for item in iterable:

Iterate over any iterable (list, tuple, dict, string, file).Example: for i, name in enumerate(names): print(i, name)

$while condition:

Repeat while condition is True. Use break to exit early.Example: while len(queue) > 0: item = queue.pop() process(item)

$match value:

Structural pattern matching (Python 3.10+). Like switch but more powerful.Example: match status: case 200: print("OK") case 404: print("Not found")

Comprehensions

$[x**2 for x in range(10)]

List comprehension — concise way to build lists from iterables.Example: [n for n in range(50) if n % 2 == 0]

${k: v for k, v in pairs}

Dict comprehension — build dictionaries from key-value pairs.Example: {x: x**2 for x in range(5)}

${x for x in items if x > 0}

Set comprehension — build sets with filtering.Example: {len(w) for w in words}

Functions & Lambdas

$def func(param: type) -> return_type:

Define a function with optional type annotations.Example: def add(a: int, b: int) -> int: return a + b

$lambda x: x * 2

Anonymous inline function. Often used with map, filter, sorted.Example: sorted(items, key=lambda x: x["age"])

$def func(*args, **kwargs):

*args captures positional excess, **kwargs captures keyword excess.Example: def log(msg, *tags, **meta): print(tags, meta)

File I/O & Context Managers

$with open("file.txt") as f:

Context manager for safe file handling. Auto-closes on block exit.Example: with open("data.json") as f: data = json.load(f)

$open("file.txt", "w") as f:

Open a file in write mode ("w"), append ("a"), or read ("r", default).Example: with open("out.txt", "w") as f: f.write("Hello")

Modules & Error Handling

$import module

Import a module. Use from x import y for specific names.Example: import json from pathlib import Path

$try/except/finally

Catch and handle exceptions. Finally always runs.Example: try: x = 1 / 0 except ZeroDivisionError: print("Cannot divide by zero")

$raise ValueError("msg")

Manually raise an exception with a descriptive message.Example: if not isinstance(x, int): raise TypeError("Expected int")

Python Cheatsheet

Modern Python — data types, control flow, comprehensions, functions, modules, and file I/O.

All examples assume Python 3.10+ with modern typing support.

Data Types & Structures

x = 42 # int — Python is dynamically typed. Variables are assigned without type declarations.

Example: name: str = "Alice" # Optional type hint

my_list = [1, 2, 3] — A list is an ordered, mutable collection. Supports mixed types.

Example: items = [1, "hello", 3.14]

my_dict = {"key": "value"} — A dict stores key-value pairs. Keys must be hashable (strings, numbers, tuples).

Example: user = {"name": "Alice", "age": 30}

my_set = {1, 2, 3} — A set is an unordered collection of unique elements. Great for membership tests.

Example: unique_ids = {101, 102, 103}

from typing import Optional — Type hints for better IDE support and static analysis. No runtime effect.

Example: def greet(name: str) -> str: return f"Hello {name}"

class MyClass: — Define a class. Modern Python uses __init__ for constructor.

Example: class User: def __init__(self, name): self.name = name

@dataclass — Auto-generate __init__, __repr__, __eq__ for data-holding classes.

Example: @dataclass class Point: x: float y: float

Strings & f-strings

f"Hello {name}, age {age}" — f-strings — embed expressions in string literals with {}.

Example: f"User {user['name']} is {user['age']} years old"

" ".join(["a", "b", "c"]) — Join a list of strings into a single string with a separator.

Example: ", ".join(["red", "green", "blue"])

"hello world".split() — Split a string on whitespace (default) or a delimiter.

Example: "a,b,c".split(",")

Control Flow & Loops

if/elif/else — Conditional branching with elif (not else if or elsif).

Example: if x > 0: print("positive") elif x == 0: print("zero") else: print("negative")

for item in iterable: — Iterate over any iterable (list, tuple, dict, string, file).

Example: for i, name in enumerate(names): print(i, name)

while condition: — Repeat while condition is True. Use break to exit early.

Example: while len(queue) > 0: item = queue.pop() process(item)

match value: — Structural pattern matching (Python 3.10+). Like switch but more powerful.

Example: match status: case 200: print("OK") case 404: print("Not found")

Comprehensions

[x**2 for x in range(10)] — List comprehension — concise way to build lists from iterables.

Example: [n for n in range(50) if n % 2 == 0]

{k: v for k, v in pairs} — Dict comprehension — build dictionaries from key-value pairs.

Example: {x: x**2 for x in range(5)}

{x for x in items if x > 0} — Set comprehension — build sets with filtering.

Example: {len(w) for w in words}

Functions & Lambdas

def func(param: type) -> return_type: — Define a function with optional type annotations.

Example: def add(a: int, b: int) -> int: return a + b

lambda x: x * 2 — Anonymous inline function. Often used with map, filter, sorted.

Example: sorted(items, key=lambda x: x["age"])

def func(*args, **kwargs): — *args captures positional excess, **kwargs captures keyword excess.

Example: def log(msg, *tags, **meta): print(tags, meta)

File I/O & Context Managers

with open("file.txt") as f: — Context manager for safe file handling. Auto-closes on block exit.

Example: with open("data.json") as f: data = json.load(f)

open("file.txt", "w") as f: — Open a file in write mode ("w"), append ("a"), or read ("r", default).

Example: with open("out.txt", "w") as f: f.write("Hello")

Modules & Error Handling

import module — Import a module. Use from x import y for specific names.

Example: import json from pathlib import Path

try/except/finally — Catch and handle exceptions. Finally always runs.

Example: try: x = 1 / 0 except ZeroDivisionError: print("Cannot divide by zero")

raise ValueError("msg") — Manually raise an exception with a descriptive message.

Example: if not isinstance(x, int): raise TypeError("Expected int")