Standard-Library Selections¶

Check the standard library before adding a dependency or writing infrastructure code. These selections cover commonly overlooked tools and choices that are easy to get wrong.

Preferred Selections¶

Need	Prefer	Notes
Filesystem paths	`pathlib.Path`	Compose and inspect paths without manual separator handling.
Packaged files	`importlib.resources`	Works for installed packages that are not ordinary filesystem directories.
Temporary files	`tempfile`	Handles secure creation and cleanup; avoid predictable names.
TOML input	`tomllib`	Built-in reader on Python 3.11+; it does not write TOML.
Time zones	`zoneinfo`	Use aware datetimes for instants crossing system boundaries.
Decimal contracts	`decimal.Decimal`	Construct from strings when exact decimal input matters.
String-valued enums	`enum.StrEnum`	Available on Python 3.11+; useful for stable finite string values.
Subprocesses	`subprocess.run`	Pass an argument sequence, set a timeout, and avoid `shell=True` by default.
Dynamic cleanup	`contextlib.ExitStack`	Composes a runtime-determined set of context managers and callbacks.
Immutable records	`dataclasses`	Use `frozen=True` only when shallow immutability matches the domain.

Frequently Overlooked Gems¶

collections.Counter for multisets and frequencies; deque for efficient operations at both ends; defaultdict for uniform missing-value construction.
itertools for lazy chaining, batching, pairing, accumulation, and combinatorics. Prefer these primitives to hand-written iterator state machines.
functools.cache for unbounded memoization of pure calls and cached_property for stable per-instance computation. Confirm memory retention and invalidation semantics first.
operator functions such as itemgetter and attrgetter for declarative sort/group keys.
graphlib.TopologicalSorter for dependency ordering and cycle detection.
shlex.join for human-readable POSIX command display. It is not a reason to execute through a shell.
secrets for tokens and security-sensitive randomness; use random for simulation and non-security sampling.
uuid.uuid7 on Python 3.14+ when sortable time-based UUIDs fit the storage contract; otherwise select a UUID version intentionally.

Selection Traps¶

Path.read_text() and write_text() are convenient for bounded content, not streaming large files.
dataclasses.asdict() recursively deep-copies nested dataclasses and collections; avoid it when identity, custom serialization, or large graphs matter.
functools.cache retains arguments and results until the cache is cleared; do not put it on unbounded request-key spaces.
datetime.utcnow() returns a naive datetime. Prefer datetime.now(timezone.utc) for an aware UTC value.
pickle is not safe for untrusted data. Choose a schema-based format at trust boundaries.
subprocess argument lists prevent shell parsing, but values still require domain validation when they select files, executables, or privileged behavior.