test.py

from datetime import timedelta
from datetime import datetime

#### testing data
raw_set = [
    {"begin": "20231201", "end": "20240101", "content": "a"},
    {"begin": "20231217", "end": "20240101", "content": "a1"},
    {"begin": "20231204", "end": "20231206", "content": "b"},
    {"begin": "20231101", "end": "20231215", "content": "c"},
    {"begin": "20231101", "end": "20231214", "content": "c1"},
    {"begin": "20231202", "end": "20231217", "content": "d"},
    {"begin": "20241202", "end": "20241217", "content": "e"},
    {"begin": "20241218", "end": "20241220", "content": "e1"},
    {"begin": "20241220", "end": "20241231", "content": "e2"},
]

#### init date
data_set = [
    {
        "begin": datetime.fromisoformat(r["begin"]),
        "end": datetime.fromisoformat(r["end"]),
        "content": r["content"],
    }
    for r in raw_set
]

oneday = timedelta(days=1)

#### init date array
date_set = []

for row in data_set:
    date_set.append(row["begin"])
    date_set.append(row["end"] + oneday)

date_set.append(datetime.fromisoformat("19700101"))
date_set.append(datetime.fromisoformat("99991231"))

date_set = sorted(list(set(date_set)))

#### go!!!
result = []

for i in range(len(date_set)-1):
    busy = False
    new_row = {"begin": "", "end": "", "content": ""}

    begin_date = date_set[i]
    end_date = date_set[i+1]

    for row in data_set:
        if begin_date >= row["begin"] and begin_date <= row["end"]:
            busy = True
            new_row["content"] = new_row["content"] + row["content"] + ";"

    new_row["begin"] = begin_date
    new_row["end"] = end_date

    if busy:
        result.append(new_row)

for r in result:
    print(r)