闲话少叙，直接上代码
 
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')
 
这个函数的参数是字符串日期，比如'20180101'，返回的也是字符串的日期，函数调用如下：
 

"""
通过datetime和dateutil进行常用日期的获取
如：
今年，去年，明年
当前季度
本月，上月，去年同期，今年一月
今天，昨天，明天，
本周、本月、本季度、本年第一天，
本周、本月、本季度、本年最后一天
"""
 
import datetime
 
# 获取常用特定日期（如去年/季度/当月/本周/首日/）
 
# =======================================
# 关于年（今年，去年，明年）
# =======================================
# 今年
today = datetime.date.today()           # 都是基于today, 此时为'2019-02-22'，下同
today.year                              # out: 2019
 
# 去年
today = datetime.date.today()
today.year-1                           # out : 2018
 
# 明年
today = datetime.date.today()
today.year+1                           # out : 2020
 
 
# =======================================
# 关于季度(当前季度)
# =======================================
today = datetime.date.today()
quarter = (today.month-1) // 3 + 1
'{}Q{}'.format(today.year, quarter)          # out: '2019Q1'
 
 
# =======================================
# 关于月(本月，上月，当年1月，去年同月)
# =======================================
# 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

做数据分析绕不开“季度末”，那么Python中怎么获得当前季度最后一天的日期呢？
 
from datetime import datetime as dt
def getql():
    today=dt.now()
    quarter = (today.month-1)/3+1
    if quarter == 1:
        return dt(today.year,3,31)
    elif quarter == 2:
        return dt(today.year,6,30)
    elif quarter == 3:
        return dt(today.year,9,30)
    else:
        return dt(today.year,12,31)
 
这个办法虽然笨，但也是相当准确的。哈哈哈！

/**
 * 根据 年份 和 季度  获取 季度 第一天 和 季度 最后 一天
 * @param year
 * @param quarter
 */
function getQuartorStartDate(year,quarter) {
	let startMonth = 1;
	if(quarter == 1){
		startMonth = 1;
	}else if (quarter == 2){
		startMonth = 4;
	}else if (quarter == 3){
		startMonth = 7;
	}else if (quarter == 4){
		startMonth = 10;
	}
	let endMonth = startMonth + 2;
	if (quarter == 0){
		endMonth = 12
	}
	const startDate = year+"-"+formatDate(startMonth)+'-01';
	const endDate = year + '-' + formatDate(endMonth) + '-' +new Date(year,endMonth,0).getDate()
	console.log(startDate,endDate)
	return {startDate,endDate}
}

//格式化月和日为MM、dd
function formatDate(value){
	if(value < 10){
		value = "0" + value;
	}
	return value;
}