如何根据当前日期变量获取当前和下个月的第一个日历日

Question

I have a date variable calls today_date as below. I need to get the 1st calendar day of the current and next month. In my case, today_date is 4/17/2021, I need to create two more variables calls first_day_current which should be 4/1/2021, and first_day_next which should be 5/1/2021. Any suggestions are greatly appreciated

import datetime as dt    
today_date
'2021-04-17'

Answer 1

Getting just the first date of a month is quite simple - since it equals 1 all the time. You can even do this without needing the datetime module to simplify calculations for you, if today_date is always a string "Year-Month-Day" (or any consistent format - parse it accordingly)

today_date = '2021-04-17'
y, m, d = today_date.split('-')
first_day_current = f"{y}-{m}-01"
y, m = int(y), int(m)
first_day_next = f"{y+(m==12)}-{m%12+1}-01"

If you want to use datetime.date() , then you'll anyway have to convert the string to (year, month, date) int s to give as arguments (or do today_date = datetime.date.today() . Then .replace(day=1) to get first_day_current. datetime.timedelta can't add months (only upto weeks), so you'll need to use other libraries for this . But it's more imports and calculations to do the same thing in effect.

Answer 2

I found out pd.offsets could accomplish this task as below -

import datetime as dt 
import pandas as pd

today_date #'2021-04-17' this is a variable that is being created in the program
first_day_current = today_date.replace(day=1) # this will be 2021-04-01
next_month = first_day_current + pd.offsets.MonthBegin(n=1)
first_day_next = next_month.strftime('%Y-%m-%d') # this will be 2021-05-01