Problem of the day: What goes on sys.path first

Python practice problems

Python

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Title	Difficulty	Category
abc.ABC: abstract properties and classmethods, in the right order	Easy	Primitives
Accept broad, return narrow: group_by and merge_counts	Medium	Primitives
Accidental quadratics: an index-backed join and a streaming top-k	Medium	End-to-End
accumulate and pairwise: max drawdown in one pass	Easy	Primitives
aclosing: release the connection on break, error and cancellation	Hard	Primitives
A Fetcher Protocol three implementations can satisfy	Medium	Primitives
A @final rate limiter	Easy	Primitives
A generic Result[T, E]	Medium	Primitives
__all__, re-export rules, and the accidental public API	Medium	Framework
Amortise cents without mixing up the units	Medium	Primitives
Annotated: metadata the type checker deliberately ignores	Medium	Framework
A rate limiter with an injected clock	Medium	Primitives
A rate limiter you can test without sleeping	Hard	End-to-End
A recursive Json alias, depth and flatten	Medium	Primitives
A registry that does not prevent collection	Medium	Primitives
asdict() and astuple(): the deep-copy tax	Hard	Framework
assert_never and the event that was never handled	Medium	Primitives
asyncify: a ParamSpec wrapper that does not block the loop	Medium	Primitives
Async iterators: the paginator you can actually close	Medium	Primitives
A typed factory fixture	Hard	Primitives
Auditing a library for import-time side effects	Hard	Framework
Auditing the Any surface of a module	Medium	Framework
BackgroundTasks: strong references, and a drain that raises	Medium	Primitives
Bare except, blind except Exception, and where to catch	Medium	Primitives
Batched async stream: never yield inside a cancel scope	Hard	End-to-End
batched: page a stream, and validate before you yield	Easy	Primitives
BoundedBuffer: a blocking queue from one Condition	Medium	Primitives
Bounded concurrency and backpressure	Hard	End-to-End
BoundedCounter: check-then-act under 64 threads	Medium	Primitives
Bounds versus constraints: clamp and dedupe	Hard	Framework
cached_property: compute once, release with the instance, invalidate on demand	Medium	Primitives
cache: memoised edit distance behind a validated wrapper	Medium	Primitives
Callback protocols: closing the Callable[..., Any] hole	Medium	Framework
Capstone: a fully typed, cancellable, observable async worker pool	Hard	End-to-End
Capstone: an immutable domain model that survives review	Hard	End-to-End
Capstone: a typed, cancellable, observable worker pool	Hard	End-to-End
Capstone: break the monolith, then enforce the layering	Hard	End-to-End
Capstone: five defects, and which tool would have found each one	Hard	End-to-End
Capstone: the upload that cannot be misused	Hard	End-to-End
ChainMap: resolve config and keep the provenance	Medium	Primitives
Class patterns, __match_args__ and an expression simplifier	Medium	End-to-End
ClassVar, field(), and the counter that must reset	Easy	Primitives
Coerce to int at an untyped boundary	Medium	Primitives
contextmanager: temporarily patch an attribute, and put it back	Medium	Primitives
Converters and validate-on-assignment: what attrs buys you	Medium	Primitives
Counter: top n-grams with deterministic ties	Easy	Primitives
Dataclasses: slots, frozen, order	Easy	Primitives
@dataclass is a code generator: what it emits	Easy	Primitives
dataclass_transform (PEP 681): making your own decorator type-checkable	Hard	Framework
datetime: reject naive input, and find the next local wall clock	Hard	Primitives