core/analysis.py

from typing import Dict, List

def build_timeline(docs: List[dict]) -> Dict[str, int]:
    timeline: Dict[str, int] = {}

    for d in docs:
        year = d.get("date", "")[:4]
        if not year.isdigit():
            continue
        timeline[year] = timeline.get(year, 0) + 1

    return timeline