python 獲取某個月份第一日和最後一日日期

from datetime import datetime, date, timedelta
import calendar

def get_month_range(start_date=None):
    '''
    獲取某個月份的第一日和最後一日的日期
    :param start_date: 傳入一個datetime類型日期，返回的爲傳入時間所在月份的首日和最後一日的日期
    :return: 
    '''
    if start_date is None:
        start_date = date.today().replace(day=1)
    else:
        print(start_date.today())
        start_date = start_date.replace(day=1)
    _, days_in_month = calendar.monthrange(start_date.year, start_date.month)
    end_date = start_date + timedelta(days=days_in_month)
    return (start_date, end_date)

current_date = datetime(2019,month=6,day=13)
first_day, last_day = get_month_range(start_date=current_date)