year_fraction.py

from datetime import datetime
from math import ceil
import calendar


def dates(d1: datetime, d2: datetime) -> list:
    middle = []
    for year in range(d1.year, d2.year):
        middle.append(datetime(year, 12, 31))

    return [d1] + middle + [d2]


def year_gap(d1: datetime, d2: datetime) -> float:
    year_fraction = .0
    dates_of_interest = sorted(dates(*sorted([d1, d2])))

    i = 0
    while i < len(dates_of_interest) - 1:
        dl, dr = dates_of_interest[i], dates_of_interest[i + 1]
        year_days = 365 + 1 * calendar.isleap(dr.year)
        year_fraction += (dr - dl).days / year_days
        i += 1

    return ceil(year_fraction * 100) / 100


d1 = datetime(1991, 1, 3)
d2 = datetime(1992, 1, 25)

print(year_gap(d1, d2))  # 1.07