Offset vs Keyset Pagination in Python

"""Demonstrate pagination using offset vs keyset (cursor) approach."""

ITEMS = [
    {"id": 1, "name": "Alice"},
    {"id": 2, "name": "Bob"},
    {"id": 3, "name": "Carol"},
    {"id": 4, "name": "David"},
    {"id": 5, "name": "Eve"},
]

def offset_paginate(items, page, page_size):
    """Return a page using offset-based pagination."""
    start = (page - 1) * page_size
    return items[start:start + page_size]

def keyset_paginate(items, last_id, page_size):
    """Return a page using keyset (cursor) pagination, assuming sorted by id."""
    if last_id is None:
        return items[:page_size]
    start = next(i for i, item in enumerate(items) if item["id"] == last_id) + 1
    return items[start:start + page_size]

if __name__ == "__main__":
    print("Offset pagination:")
    for page in range(1, 4):
        result = offset_paginate(ITEMS, page, page_size=2)
        print(f"  page {page}: {[item['name'] for item in result]}")

    print("Keyset pagination:")
    cursor = None
    for _ in range(3):
        result = keyset_paginate(ITEMS, cursor, page_size=2)
        if not result:
            break
        print(f"  after {cursor}: {[item['name'] for item in result]}")
        cursor = result[-1]["id"]