How to check the date is empty using python?

问题

The startdate and enddate values are coming from jenkin to lambda. In this code I am trying to get value using event["start_date"] and event["end_date"] and it's working fine, but if startdate and enddate are not available then the code should automatically take today's and yesterday's date.

I am new to python, can someone help here?

I tried as below but I am getting error. If I will mention 'startdate and enddate is none' and set both values as none then it's working but I need to implement mentioned in code as I am using AWS lambda with python.

import datetime
from datetime import timedelta

dateformat = "%Y-%m-%d"
startdate = datetime.datetime.strptime("", dateformat)
enddate = datetime.datetime.strptime("", dateformat)
# Both startdate and enddate values come from Jenkin to lambda  - 
event["start_date"] and event["end_date"]
if (startdate and enddate) == "":
    startdate = datetime.date.today()
    enddate = startdate - datetime.timedelta(days = 1)
    print('yesterday : ', enddate)  
    print('Today : ', startdate)

Current Error Output:

Traceback (most recent call last):
  File "variable_value_change.py", line 10, in <module>
    startdate = datetime.datetime.strptime("", dateformat)
  File "C:\Users\336635743\AppData\Local\Programs\Python\Python37-32\lib\_strptime.py", line 577, in _strptime_datetime
    tt, fraction, gmtoff_fraction = _strptime(data_string, format)
  File "C:\Users\336635743\AppData\Local\Programs\Python\Python37-32\lib\_strptime.py", line 359, in _strptime
   (data_string, format))
ValueError: time data '' does not match format '%Y-%m-%d'

回答1:

Change this line

if (startdate and enddate) == "":

to

if startdate == "" and enddate == "":

Another way:

if not startdate and not enddate: # PEP 8 recommended

回答2:

Use a try-except block.

Ex:

try:
    startdate = datetime.datetime.strptime(event["start_date"], dateformat)
    enddate = datetime.datetime.strptime(event["end_Date"], dateformat)
except:
    startdate = datetime.date.today()
    enddate = startdate - datetime.timedelta(days = 1)

回答3:

This is probably not what you want:

 if (startdate and enddate) == "":

How about:

if startdate == '':
    startdate = datetime.date.today()
if enddate == '':
    enddate = startdate - datetime.timedelta(days = 1)

回答4:

I tried it other way as I was working on python AWS lambda and it works.

  if "start_date" in event:
        startdate = datetime.datetime.strptime(event["start_date"], dateformat) 
        enddate = datetime.datetime.strptime(event["end_date"], dateformat) 

来源：https://stackoverflow.com/questions/56329516/how-to-check-the-date-is-empty-using-python