1. 获取今天、昨天、明天

#coding=utf-8
 
import datetime
from datetime import timedelta
 
now = datetime.datetime.now()
 
#今天
today = now
 
#昨天
yesterday = now - timedelta(days=1)
 
#明天
tomorrow = now + timedelta(days=1)

2. 获取本周、上周、本月、上月、本季，上季、本年、上年

#本周第一天和最后一天
this_week_start = now - timedelta(days=now.weekday())
this_week_end = now + timedelta(days=6-now.weekday())
 
#上周第一天和最后一天
last_week_start = now - timedelta(days=now.weekday()+7)
last_week_end = now - timedelta(days=now.weekday()+1)
 
#本月第一天和最后一天
this_month_start = datetime.datetime(now.year, now.month, 1)
this_month_end = datetime.datetime(now.year, now.month + 1, 1) - timedelta(days=1)
 
#上月第一天和最后一天
last_month_end = this_month_start - timedelta(days=1)
last_month_start = datetime.datetime(last_month_end.year, last_month_end.month, 1)
 
#本季第一天和最后一天
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)
 
#上季第一天和最后一天
last_quarter_end = this_quarter_start - timedelta(days=1)
last_quarter_start = datetime.datetime(last_quarter_end.year, last_quarter_end.month - 2, 1)
 
#本年第一天和最后一天
this_year_start = datetime.datetime(now.year, 1, 1)
this_year_end = datetime.datetime(now.year + 1, 1, 1) - timedelta(days=1)
 
#去年第一天和最后一天
last_year_end = this_year_start - timedelta(days=1)
last_year_start = datetime.datetime(last_year_end.year, 1, 1)

3. 另外一种写法：各种日期

today = datetime.date.today()
quarter = (today.month-1) // 3 + 1
'{}Q{}'.format(today.year, quarter)          # out: '2019Q1'
 
# 本月(月份)
today = datetime.date.today()
today.month                                        # out: 2
 
# 本月(年月)
today = datetime.date.today()
datetime.datetime.strftime(today, "%Y-%m")             # out: '2019-02'
 
# 上月
today = datetime.date.today()
last_month = today + datetime.timedelta(days=-today.day)
# last_month.month                                     # 月份，out: 1
datetime.datetime.strftime(last_month,"%Y-%m")             # out: '2019-01'
 
# 上N个月
from dateutil.relativedelta import relativedelta           # 需要引入新的包
today = datetime.date.today()
last_2_month = today + relativedelta(months=-2)           # 上两个月，上N个月参数为(months=-N)
datetime.datetime.strftime(last_2_month, "%Y-%m")             # out: '2018-12'
 
# 当年1月
today = datetime.date.today()
str(today.year) +'-01'              # out: '2019-01'
 
 
# =======================================
# 关于天
# =======================================
# 今天(天数)
today = datetime.date.today()
today.day
# 今天（日期）
today.isoformat()                # out: '2019-02-22'
 
#  昨天
today = datetime.date.today()
yesterday = today + datetime.timedelta(days=-1)
yesterday.isoformat()                                   # out: '2019-02-21'
 
# 明天
today = datetime.date.today()
yesterday = today + datetime.timedelta(days=1)
yesterday.isoformat()                                   # out: '2019-02-23'
 
# 本周第一天
today = datetime.date.today()
week_start_day = today - datetime.timedelta(days=today.weekday())
week_start_day.isoformat()                                   # '2019-02-18'，周一
 
# 本周最后一天
today = datetime.date.today()
week_end_day = today + datetime.timedelta(days=6-today.weekday())
week_end_day.isoformat()                                   # '2019-02-24'，周天
 
# 本月第一天
today = datetime.date.today()
month_start_day = today - datetime.timedelta(days=today.day-1)
month_start_day.isoformat()                                   # '2019-02-01'，当月第一天
 
# 本月最后一天
from dateutil.relativedelta import relativedelta            # 引入新的包
today = datetime.date.today()
# 必须先置为首日，直接用relativedelta(months=1,days=-today.day+1)会有错误结果
month_end_day = (today + datetime.timedelta(days=-today.day+1)) + relativedelta(months=1,days=-1)
month_end_day.isoformat()                                    # '2019-02-28'，当月最后一天
 
# 本季度第一天
today = datetime.date.today()
quarter_start_day = datetime.date(today.year,today.month - (today.month - 1) % 3, 1)
quarter_start_day.isoformat()                              # '2019-01-01'  ，本季度第一天
 
# 本季度最后一天
from dateutil.relativedelta import relativedelta           # 引入新的包
today = datetime.date.today()
quarter_end_day = datetime.date(today.year,today.month - (today.month - 1) % 3 +2, 1) + relativedelta(months=1,days=-1)
quarter_end_day.isoformat()                                # '2019-03-31'  ，本季度最后一天
 
# 本年第一天
today = datetime.date.today()
year_start_day = datetime.date(today.year, 1, 1)
year_start_day.isoformat()                                      # '2019-01-01'  ，本年第一天
 
# 本年最后一天
today = datetime.date.today()
year_end_day = datetime.date(today.year+1, 1, 1) - datetime.timedelta(days=1)
year_end_day.isoformat()                                        # '2019-12-31' ，本年最后一天

4. 另一种写法：获取上一季度最后一天

from datetime import datetime
def getlastseason(today):
    today = datetime.strptime(today, '%Y%m%d')
    quarter = (today.month - 1) / 3 + 1
    if quarter == 1:
        return datetime(today.year - 1, 12, 31).strftime('%Y%m%d')
    elif quarter == 2:
        return datetime(today.year, 3, 31).strftime('%Y%m%d')
    elif quarter == 3:
        return datetime(today.year, 6, 30).strftime('%Y%m%d')
    else:
        return datetime(today.year, 9, 30).strftime('%Y%m%d')