paradox.py

from datetime import date, timedelta


class Day(date):

    @property
    def 的昨天(self):
        return self + timedelta(days=-1)

    @property
    def 的明天(self):
        return self + timedelta(days=1)


if __name__ == '__main__':

    理想的今天 = Day(year=2020, month=4, day=18)  # a Sunday

    # case A
    现实的今天 = Day(year=2020, month=4, day=16)  # a Friday
    # "如果昨天是明天的话就好了"
    assert 理想的今天.的昨天 == 现实的今天.的明天

    # =====================================
    # case B
    现实的今天 = Day(year=2020, month=4, day=20)  # a Tuesday
    # "如果昨天是明天的话就好了"
    assert 现实的今天.的昨天 == 理想的今天.的明天