datetime的代码解析

有关datetime应用例子的代码解析

import numpy as np
import datetime

def call(self, database_folder='', shapefile='', track_no='',
start_date='', end_date='', start_dates='', end_dates='', date='', dates='',
time_window='', mode='IW', product_type='SLC', polarisation='VV'):
# Run the different commands step by step

# Create a list of search windows with start and end dates
if isinstance(date, datetime.datetime):
    dates = [date]
elif isinstance(dates, datetime.datetime):
    dates = [dates]

if isinstance(dates, list):
    for date in dates:
        if not isinstance(date, datetime.datetime):
            raise TypeError('Input dates should be datetime objects.')

    if isinstance(time_window, datetime.timedelta):
        self.start_dates = [date - time_window for date in dates]
        self.end_dates = [date + time_window for date in dates]
    else:
        self.start_dates = [date.replace(hour=0, minute=0, second=0, microsecond=0) for date in dates]
        self.end_dates = [date + datetime.timedelta(days=1) for date in self.start_dates]

elif isinstance(start_date, datetime.datetime) and isinstance(end_date, datetime.datetime):
    self.start_dates = [start_date]
    self.end_dates = [end_date]
elif isinstance(start_dates, list) and isinstance(end_dates, list):
    self.start_dates = start_dates
    self.end_dates = end_dates
    valid_dates = [isinstance(start_date, datetime.datetime) * isinstance(end_date, datetime.datetime) for
                   start_date, end_date in zip(start_dates, end_dates)]
    if np.sum(valid_dates) < len(valid_dates):
        raise TypeError('Input dates should be datetime objects.')
else:
    raise TypeError('You should define a start or end date or a list of dates to search for Sentinel-1 data! '
                    'Dates should be datetime objects')

self.start_dates = np.array(self.start_dates)
self.end_dates = np.array(self.end_dates)

# 其他与本讨论无关的逻辑
self.other_concrete_logics()
从前没用过dateltime读不懂，讲一下核心逻辑和修改建议即可，谢谢！

1.这段代码的核心逻辑是要做什么
2.请画出核心逻辑的流程图；
3.这段代码（你觉得）有什么写得好或可以改进的地方？

datetime是个包
datetime.datetime是个类
那么它的实例实际上就是个时间类型的对象
datetime相加相减之后会是个datetime.timedelta类型的对象
同样的，datetime类型可以和timedelta相加减，结果会是个datetime类型
-=-=-=
你可以将datetime理解为带日期的时间，而timedelta就是时间差
-=-=-=
代码先是各种判断传入的参数到底是不是要求的类型，不是就抛错误
各种if其实就是允许传入的dates是各种类型，如果是list那就用列表推导式计算date - time_window和date + time_window，分别放入两个列表，一个作为starttime，一个作为endtime
如果传入的dates不是个list而只start_date是一个datetime，那就self.start_dates里只放一项
如果dates不是list，start_date也不是datetime，而是个list，那就直接把start_dates赋值给self.start_dates
如果都不是，抛出异常