144 commands · 9 cheat sheets · Python

Language and Objects master quick reference

Browse 144 commands from 9 focused cheat sheets on page 1 of 1. Each example opens its matching detailed section.

Language and Objects · 16 commands

Python Classes and Dataclasses Cheat Sheet

Use	Syntax	Examples
Define a class	`class Account: pass`	View examples
Initialize instance state	`def __init__(self, owner): self.owner = owner`	View examples
Define instance behavior	`def deposit(self, amount): self.balance += amount`	View examples
Define shared state	`class Account: currency = 'USD'`	View examples
Add an alternate constructor	`@classmethod`	View examples
Attach a utility	`@staticmethod`	View examples
Expose computed state	`@property`	View examples
Create a subclass	`class Admin(User): pass`	View examples
Delegate through the MRO	`super().__init__(name)`	View examples
Test compatible type	`isinstance(user, User)`	View examples
Generate record methods	`@dataclass`	View examples
Create a fresh mutable default	`tags: list[str] = field(default_factory=list)`	View examples
Emulate immutability	`@dataclass(frozen=True)`	View examples
Generate slots	`@dataclass(slots=True)`	View examples
Convert fields recursively	`payload = asdict(order)`	View examples
Copy with changes	`updated = replace(item, price=12)`	View examples

Language and Objects · 11 commands

Python Context Managers Cheat Sheet

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Use	Syntax	Examples
Manage one resource	`with open(path, encoding='utf-8') as file: data = file.read()`	View examples
Manage several resources	`with open(source) as src, open(target, 'w') as dst: copy(src, dst)`	View examples
Return an acquired resource	`def __enter__(self): return self.resource`	View examples
Handle exit	`def __exit__(self, exc_type, exc, traceback): self.close()`	View examples
Create from a generator	`@contextmanager`	View examples
Close an object	`with closing(resource) as value: use(value)`	View examples
Suppress selected errors	`with suppress(FileNotFoundError): path.unlink()`	View examples
Redirect standard output	`with redirect_stdout(buffer): print('captured')`	View examples
Manage dynamic contexts	`with ExitStack() as stack: files = [stack.enter_context(open(p)) for p in paths]`	View examples
Register cleanup	`stack.callback(cleanup, resource)`	View examples
Use optional context	`manager = open(path) if path else nullcontext(sys.stdout)`	View examples

Language and Objects · 17 commands

Python Decorators, Closures, and Callables Cheat Sheet

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Use	Syntax	Examples
Return a closure	`return inner`	View examples
Rebind enclosing state	`nonlocal count`	View examples
Inspect captured values	`values = function.__closure__`	View examples
Apply a decorator	`@decorator`	View examples
Preserve wrapper metadata	`@wraps(function)`	View examples
Reach the wrapped callable	`original = decorated.__wrapped__`	View examples
Configure a decorator	`@repeat(times=3)`	View examples
Stack decorators	`result = outer(inner(function))`	View examples
Make instances callable	`def __call__(self, value): return self.prefix + value`	View examples
Check callability	`supported = callable(value)`	View examples
Bind selected arguments	`configured = partial(function, fixed_arg, option=value)`	View examples
Bind arguments on methods	`method = partialmethod(function, fixed_arg)`	View examples
Register a type implementation	`@render.register(str)`	View examples
Inspect dispatch resolution	`implementation = render.dispatch(value_type)`	View examples
Memoize bounded results	`@lru_cache(maxsize=128)`	View examples
Clear a function cache	`function.cache_clear()`	View examples
Inspect cache statistics	`stats = function.cache_info()`	View examples

Language and Objects · 18 commands

Python Enums and Symbolic Constants Cheat Sheet

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Use	Syntax	Examples
Declare an enum	`class Color(Enum): RED = 1`	View examples
Look up by value	`member = Color(1)`	View examples
Look up by name	`member = Color['RED']`	View examples
Read member metadata	`name, value = member.name, member.value`	View examples
Iterate canonical members	`members = list(Color)`	View examples
Declare an alias	`CRIMSON = RED`	View examples
Inspect names including aliases	`names = Color.__members__`	View examples
Reject duplicate values	`@unique`	View examples
Generate enum values	`PENDING = auto()`	View examples
Create string-compatible members	`class Format(StrEnum): JSON = auto()`	View examples
Create integer-compatible members	`class ExitCode(IntEnum): OK = 0`	View examples
Declare bit flags	`class Permission(Flag): READ = auto()`	View examples
Combine flags	`access = Permission.READ \| Permission.WRITE`	View examples
Test a contained flag	`allowed = Permission.WRITE in access`	View examples
Customize missing-value lookup	`_missing_ = classmethod(normalize_missing_value)`	View examples
Add member behavior	`def can_retry(self): return self is State.FAILED`	View examples
Build an enum dynamically	`Level = Enum('Level', ['LOW', 'HIGH'])`	View examples
Verify enum constraints	`@verify(CONTINUOUS)`	View examples

Language and Objects · 15 commands

Python Exceptions Cheat Sheet

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Use	Syntax	Examples
Catch one exception	`except ValueError: number = 0`	View examples
Inspect an exception	`except ValueError as error: print(error)`	View examples
Catch related failures	`except (TypeError, ValueError) as error: print(error)`	View examples
Use ordered handlers	`except FileNotFoundError: use_default()`	View examples
Run after success	`else: print(value)`	View examples
Always clean up	`finally: resource.close()`	View examples
Raise an exception	`raise ValueError("quantity must be positive")`	View examples
Re-raise the current error	`except OSError: log_failure(); raise`	View examples
Chain a domain error	`raise ConfigError("invalid port") from error`	View examples
Hide incidental context	`raise ValueError("unknown user") from None`	View examples
Define a custom exception	`class ConfigError(Exception): pass`	View examples
Store error context	`error = ValidationError(field="email", message="invalid address")`	View examples
Convert at a boundary	`value = int(text)`	View examples
Use managed cleanup	`with open("settings.txt", encoding="utf-8") as file: data = file.read()`	View examples
Assert an invariant	`assert total >= 0, "total cannot be negative"`	View examples

Language and Objects · 19 commands

Python Functions Cheat Sheet

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Use	Syntax	Examples
Define a function	`def greet(name): return f"Hello, {name}!"`	View examples
Call a function	`message = greet("Ada")`	View examples
Set a default value	`def greet(name, punctuation="!"): return f"Hello, {name}{punctuation}"`	View examples
Pass a keyword argument	`message = greet(name="Ada", punctuation=".")`	View examples
Require a positional input	`def ratio(value, total, /): return value / total`	View examples
Require a keyword input	`def connect(host, *, timeout=10): return f"{host}:{timeout}"`	View examples
Create a fresh default list	`def collect(value, items=None): items = [] if items is None else items items.append(value) return items`	View examples
Collect positional arguments	`def total(*values): return sum(values)`	View examples
Collect keyword arguments	`def profile(**fields): return fields`	View examples
Unpack positional values	`result = total(*[4, 6, 10])`	View examples
Unpack keyword values	`user = profile(**{"name": "Ada", "role": "engineer"})`	View examples
Annotate a function	`def area(width: float, height: float) -> float: return width * height`	View examples
Add a docstring	`def area(width, height): """Return a rectangle's area.""" return width * height`	View examples
Return a value	`def double(number): return number * 2`	View examples
Return several values	`def bounds(values): return min(values), max(values)`	View examples
Pass a callback	`labels = list(map(str.upper, ["draft", "ready"]))`	View examples
Create a small lambda	`users.sort(key=lambda user: user["name"])`	View examples
Return a closure	`def multiplier(factor): return lambda value: value * factor`	View examples
Wrap a function	`greet = trace(greet)`	View examples

Language and Objects · 18 commands

Python Object Protocols and Special Methods Cheat Sheet

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Use	Syntax	Examples
Define developer representation	`def __repr__(self): return f'Type({self.value!r})'`	View examples
Define readable text	`def __str__(self): return self.label`	View examples
Define truth testing	`def __bool__(self): return self.is_ready`	View examples
Define equality	`def __eq__(self, other): return self.value == other.value if isinstance(other, Type) else NotImplemented`	View examples
Define hashing	`def __hash__(self): return hash((self.first, self.second))`	View examples
Decline an operation	`return NotImplemented`	View examples
Define less-than ordering	`def __lt__(self, other): return self.value < other.value if isinstance(other, Type) else NotImplemented`	View examples
Define addition	`def __add__(self, other): return type(self)(self.value + other.value)`	View examples
Define reflected addition	`def __radd__(self, other): return type(self)(other + self.value)`	View examples
Report container length	`def __len__(self): return len(self._items)`	View examples
Support indexed access	`def __getitem__(self, key): return self._items[key]`	View examples
Optimize membership	`def __contains__(self, item): return item in self._items`	View examples
Provide iteration	`def __iter__(self): return iter(self._items)`	View examples
Manage one attribute	`value = property(getter, setter)`	View examples
Handle missing attributes	`def __getattr__(self, name): return self.fields[name]`	View examples
Intercept all instance lookup	`def __getattribute__(self, name): return object.__getattribute__(self, name)`	View examples
Define descriptor reading	`def __get__(self, instance, owner=None): return self if instance is None else instance.__dict__[self.name]`	View examples
Learn the assigned name	`def __set_name__(self, owner, name): self.name = name`	View examples

Language and Objects · 16 commands

Python Structural Pattern Matching Cheat Sheet

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Use	Syntax	Examples
Match a literal	`case 200:`	View examples
Capture the subject	`case value:`	View examples
Ignore the subject	`case _:`	View examples
Match a fixed sequence	`case [command, target]:`	View examples
Capture remaining items	`case [head, *middle, tail]:`	View examples
Match a command prefix	`case ['deploy', environment, *flags]:`	View examples
Require mapping keys	`case {'event': 'login', 'user': user}:`	View examples
Capture extra mapping entries	`case {'event': kind, **metadata}:`	View examples
Match class attributes positionally	`case Point(0, y):`	View examples
Match class attributes by name	`case Point(x=x, y=0):`	View examples
Match alternatives	`case 401 \| 403:`	View examples
Capture across alternatives	`case ('get', path) \| ('delete', path):`	View examples
Keep a matched value	`case (401 \| 403) as status:`	View examples
Add a guard	`case {'score': score} if score >= 80:`	View examples
Match a symbolic constant	`case Status.READY:`	View examples
Match nested structures	`case {'type': 'move', 'point': [x, y]}:`	View examples

Language and Objects · 14 commands

Python Type Hints, Generics, and Protocols Cheat Sheet

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Use	Syntax	Examples
Annotate a function	`def total(values: list[float]) -> float: ...`	View examples
No return value	`def log(message: str) -> None: ...`	View examples
Union type	`identifier: int \| str`	View examples
Optional value	`name: str \| None = None`	View examples
Narrow by runtime type	`if isinstance(value, str): return value.casefold()`	View examples
Read-only collection input	`def first(values: Sequence[str]) -> str: ...`	View examples
Read-only mapping input	`def render(values: Mapping[str, object]) -> str: ...`	View examples
Callable signature	`transform: Callable[[str], str]`	View examples
Declare a type alias	`type UserId = int`	View examples
Typed dictionary shape	`class UserRow(TypedDict): ...`	View examples
Generic type parameter	`def first[T](values: Sequence[T]) -> T: ...`	View examples
Structural protocol	`class SupportsClose(Protocol): ...`	View examples
Runtime protocol check	`@runtime_checkable`	View examples
User-defined narrowing	`def is_str_list(value: list[object]) -> TypeGuard[list[str]]: ...`	View examples

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