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How to Use MappingProxyType to Create Immutable Dict Views in Python
Create a read-only, immutable view of a dictionary using MappingProxyType from the types module, while the original dict stays mutable.
from types import MappingProxyType
config = {"debug": True, "port": 8080}
# Create an immutable read-only view of the dict
read_only_config = MappingProxyType(config)
print(f"Read-only value: {read_only_config['debug']}")
print(f"Dict is mapping: {isinstance(read_only_config, dict)}")
# Original dict can still be …How to Use a Frozenset as a Dict Key in Python
Demonstrates using an immutable frozenset as a hashable dictionary key, including equality and lookup with differently-ordered elements.
frozen = frozenset({"a", "b", "c"})
mapping = {frozen: "set as hashable key"}
other_frozen = frozenset(["c", "b", "a"])
print(f"Are keys equal? {frozen == other_frozen}")
print(f"Lookup with different order: {mapping[other_frozen]}")
print(f"Hash matches: {hash(frozen) == hash(other_frozen)}")How to Create Immutable Data Classes with frozen=True in Python
Create immutable data classes in Python using @dataclass(frozen=True) to prevent attribute modifications after instantiation.
from dataclasses import dataclass
@dataclass(frozen=True)
class Point:
x: float
y: float
def distance_from_origin(self) -> float:
return (self.x**2 + self.y**2) ** 0.5
if __name__ == "__main__":
p = Point(3.0, 4.0)
print(p)
print(f"Distance from origin: {p.distance_from_origin():.2f}…How to Create an Immutable Money Class in Python with dataclasses
Define a frozen dataclass Money that holds an amount and currency, enforces non-negative amounts, and supports safe addition across matching currencies.
from dataclasses import dataclass
@dataclass(frozen=True)
class Money:
amount: float
currency: str = "USD"
def __post_init__(self) -> None:
if self.amount < 0:
raise ValueError("amount must be non-negative")
def add(self, other: "Money") -> "Money":
if self.currency != o…How to Use NamedTuples for Lightweight Records in Python
Create lightweight, immutable data records with namedtuple that behave like tuples but have named fields for improved readability and access.
from collections import namedtuple
Point = namedtuple("Point", ["x", "y"])
p = Point(3, 4)
print(p)
print(p.x, p.y)
print(p[0], p[1])
x, y = p
print(x, y)
print(p._asdict())
p2 = p._replace(x=10)
print(p2)
if __name__ == "__main__":
print("NamedTuple demo complete")NamedTuple typed record in Python
Define a lightweight immutable record with type hints using typing.NamedTuple; access fields by name and unpack like a tuple.
from typing import NamedTuple
class Point(NamedTuple):
x: float
y: float
label: str = "origin"
if __name__ == "__main__":
p = Point(3.5, -2.0, "A")
print(p)
print(f"x={p.x}, y={p.y}, label={p.label}")
print("is tuple:", isinstance(p, tuple))
q = Point(1.0, 1.0)
print(q)
# …How to Build an Immutable Money Value Object in Python
Implement an immutable Money class with rounded decimal amounts, currency, safe equality, and hashing for use as a value object.
class Money:
def __init__(self, amount: float, currency: str):
object.__setattr__(self, "_amount", round(amount, 2))
object.__setattr__(self, "_currency", currency)
def __setattr__(self, name, value):
raise AttributeError(f"Money is immutable: cannot set '{name}'")
def __delattr__…How to Implement the Flyweight Pattern in Python
Implements the Flyweight design pattern to share immutable intrinsic state (character + font) across many document objects, reducing memory usage.
class Character:
"""Flyweight - stores only intrinsic state (shared)."""
def __init__(self, char: str, font: str):
self.char = char
self.font = font
def render(self, size: int) -> str:
return f"{self.char}_{self.font}_{size}"
class CharacterFactory:
"""Flyweight factory - ma…How to Take Periodic Snapshots of Aggregate State in Python
Build a Python class that accumulates values and periodically captures immutable snapshots of total, count, and average for later analysis.
import time
import random
from collections import defaultdict
class SnapshotAggregator:
def __init__(self):
self.total = 0
self.count = 0
self.history = []
def add(self, value):
self.total += value
self.count += 1
def snapshot(self):
avg = self.total / se…How to Replace Fields in an Immutable Dataclass in Python
Create a new copy of a frozen dataclass with selected fields changed, leaving the original unchanged.
from dataclasses import dataclass, replace
@dataclass(frozen=True)
class ServerConfig:
name: str
cpu: int = 2
ram: int = 4096
tags: tuple = ()
original = ServerConfig("web-01", cpu=4, tags=("env:prod",))
updated = replace(original, ram=8192, tags=("env:prod", "region:us-east"))
print("Original:", …Browse by section
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