dataclasses, enum & contextlib

dataclasses reduce boilerplate for data objects. enum gives named constants with type safety. contextlib simplifies context managers (contextmanager, suppress, ExitStack).

Recipe

from dataclasses import dataclass
from enum import StrEnum
from contextlib import contextmanager
 
class Status(StrEnum):
    PENDING = "pending"
    DONE = "done"
 
@dataclass(frozen=True)
class Job:
    id: int
    status: Status = Status.PENDING

When to reach for this:

• DTOs and config records -> dataclass
• Mode/state constants -> StrEnum
• Quick resource scopes -> @contextmanager
• Optional file absent -> suppress(FileNotFoundError)
• Many nested managers -> ExitStack

Working Example

from contextlib import contextmanager, suppress
from dataclasses import dataclass, field
from enum import StrEnum
 
class Role(StrEnum):
    ADMIN = "admin"
    USER = "user"
 
@dataclass
class Account:
    email: str
    role: Role = Role.USER
    tags: list[str] = field(default_factory=list)
 
@contextmanager
def temp_role(account: Account, role: Role):
    old = account.role
    account.role = role
    try:
        yield account
    finally:
        account.role = old
 
ada = Account("ada@example.com")
with temp_role(ada, Role.ADMIN):
    print("elevated", ada.role)
print("restored", ada.role)
 
with suppress(FileNotFoundError):
    open("missing.cfg").read()

What this demonstrates:

• frozen=True for immutable value objects
• field(default_factory=list) avoids mutable default pitfall
• StrEnum serializes cleanly to JSON strings
• contextmanager for reversible temporary state

Deep Dive

dataclass options

• slots=True (3.10+) memory savings
• kw_only=True (3.10+) explicit construction
• __post_init__ validation

enum flavors

• StrEnum for JSON APIs
• IntEnum for numeric codes
• @unique decorator prevents alias duplicates

Gotchas

• Mutable dataclass as dict key - unhashable unless frozen. Fix: frozen=True or don't key by instance.
• Enum comparison to raw string - StrEnum compares equal to str in 3.11+ but be explicit in APIs. Fix: type hints Role not str.
• contextmanager without try/finally - teardown skipped on error. Fix: wrap yield in try/finally.
• ExitStack forgotten - manual close errors. Fix: always with ExitStack().
• dataclass vs Pydantic - dataclass no validation. Fix: Pydantic at HTTP boundary.

Alternatives

FAQs

Related

• Context Managers as a Pattern - pattern depth
• json & Serialization - StrEnum in JSON
• collections recap - Counter with enums
• Standard Library Best Practices - ergonomic rules

Stack versions: This page was written for Python 3.14.0 (stable 3.14, maintenance 3.13), FastAPI 0.115+, Django 5.2, Flask 3.1, Pydantic 2, PyTorch 2.6+, pandas 2.2+, Polars 1.x, ruff 0.9+, and uv 0.6+.