philippe philippe - 3 months ago 15
Python Question

python date of the previous month

I am trying to get the date of the previous month with python.
Here is what i've tried:

str( time.strftime('%Y') ) + str( int(time.strftime('%m'))-1 )


However, this way is bad for 2 reasons: First it returns 20122 for the February of 2012 (instead of 201202) and secondly it will return 0 instead of 12 on January.

I have solved this trouble in bash with

echo $(date -d"3 month ago" "+%G%m%d")


I think that if bash has a built-in way for this purpose, then python, much more equipped, should provide something better than forcing writing one's own script to achieve this goal. Of course i could do something like:

if int(time.strftime('%m')) == 1:
return '12'
else:
if int(time.strftime('%m')) < 10:
return '0'+str(time.strftime('%m')-1)
else:
return str(time.strftime('%m') -1)


I have not tested this code and i don't want to use it anyway (unless I can't find any other way:/)

Thanks for your help!

Answer

datetime and the datetime.timedelta classes are your friend.

  1. find today.
  2. use that to find the first day of this month.
  3. use timedelta to backup a single day, to the last day of the previous month.
  4. print the YYYYMM string you're looking for.

Like this:

 >>> import datetime
 >>> today = datetime.date.today()
 >>> first = today.replace(day=1)
 >>> lastMonth = first - datetime.timedelta(days=1)
 >>> print lastMonth.strftime("%Y%m")
 201202
 >>>