python python日付アルゴリズム今週、先週、今月、先月、今季、前期、今年、昨年

import datetime
from datetime import timedelta
now = datetime.datetime.now()
#  
today = now
#  
yesterday = now - timedelta(days=1)
#  
tomorrow = now + timedelta(days=1)

#     
now_quarter = now.month / 3 if now.month % 3 == 0 else now.month / 3 + 1
#          
this_week_start = now - timedelta(days=now.weekday())
this_week_end = now + timedelta(days=6-now.weekday())
#          
last_week_start = now - timedelta(days=now.weekday()+7)
last_week_end = now - timedelta(days=now.weekday()+1)
#          
this_month_start = datetime.datetime(now.year, now.month, 1)
this_month_end = datetime.datetime(now.year, now.month + 1, 1) - timedelta(days=1)
#          
last_month_end = this_month_start - timedelta(days=1)
last_month_start = datetime.datetime(last_month_end.year, last_month_end.month, 1)
#          
month = (now.month - 1) - (now.month - 1) % 3 + 1
this_quarter_start = datetime.datetime(now.year, month, 1)
this_quarter_end = datetime.datetime(now.year, month + 3, 1) - timedelta(days=1)
#          
last_quarter_end = this_quarter_start - timedelta(days=1)
last_quarter_start = datetime.datetime(last_quarter_end.year, last_quarter_end.month - 2, 1)
 #          
this_year_start = datetime.datetime(now.year, 1, 1)
this_year_end = datetime.datetime(now.year + 1, 1, 1) - timedelta(days=1)

#          
last_year_end = this_year_start - timedelta(days=1)
last_year_start = datetime.datetime(last_year_end.year, 1, 1)