Comprehensions Over Records

mediumpy_datastructures

Ten little extractors over a hit-log: each record is a dict with EventID, EventTime, UserID, PageID, RegionID (may be None), DeviceType. Write each as a single comprehension — no for/while loops and no map/filter:

get_unique_page_ids — set of all PageIDs.
get_unique_page_ids_visited_after_ts(records, ts) — PageIDs with EventTime > ts.
get_unique_user_ids_visited_page_after_ts(records, ts, page_id) — UserIDs that hit page_id after ts.
get_events_by_device_type(records, device_type) — records with that device (order preserved).
get_region_ids_with_none_replaces_by_default(records) — each RegionID, with None → DEFAULT_REGION_ID (100500).
get_region_id_if_not_none(records) — the non-None RegionIDs.
get_keys_where_value_is_not_none(r) — keys of a record with a non-None value.
get_record_with_none_if_key_not_in_keys(r, keys) — same record, values whose key isn't in keys set to None.
get_record_with_key_in_keys(r, keys) — the record restricted to keys.
get_keys_if_key_in_keys(r, keys) — the record's keys that are in keys.

Constraints

no map, filter
no for/while loops

Your solution

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Hints

Hint 1

Each function is one list/set/dict comprehension over the records — e.g. {r['PageID'] for r in records}.

Hint 2

Add an `if` clause to filter; use a conditional expression (a if cond else b) for the default-value cases.

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