How to find the date n days ago in Python?

问题

Good evening chaps,

I would like to write a script where I give python a number of days (let s call it d) and it gives me the date we were d days ago.

I am struggling with the module datetime:

import datetime 

tod = datetime.datetime.now()
d = timedelta(days = 50) 
a = tod - h 
Type Error : unsupported operand type for - : "datetime.timedelta" and 
"datetime.datetime"

Thanks for your help

回答1:

You have mixed something up with your variables, you can subtract timedelta d from datetime.datetime.now() with no issue:

import datetime 
tod = datetime.datetime.now()
d = datetime.timedelta(days = 50)
a = tod - d
print(a)
2014-12-13 22:45:01.743172

回答2:

If your arguments are something like, yesterday,2 days ago, 3 months ago, 2 years ago. The function below could be of help in getting the exact date for the arguments. You first need to import the following date utils

import datetime
from dateutil.relativedelta import relativedelta

Then implement the function below

def get_past_date(str_days_ago):
    TODAY = datetime.date.today()
    splitted = str_days_ago.split()
    if len(splitted) == 1 and splitted[0].lower() == 'today':
        return str(TODAY.isoformat())
    elif len(splitted) == 1 and splitted[0].lower() == 'yesterday':
        date = TODAY - relativedelta(days=1)
        return str(date.isoformat())
    elif splitted[1].lower() in ['hour', 'hours', 'hr', 'hrs', 'h']:
        date = datetime.datetime.now() - relativedelta(hours=int(splitted[0]))
        return str(date.date().isoformat())
    elif splitted[1].lower() in ['day', 'days', 'd']:
        date = TODAY - relativedelta(days=int(splitted[0]))
        return str(date.isoformat())
    elif splitted[1].lower() in ['wk', 'wks', 'week', 'weeks', 'w']:
        date = TODAY - relativedelta(weeks=int(splitted[0]))
        return str(date.isoformat())
    elif splitted[1].lower() in ['mon', 'mons', 'month', 'months', 'm']:
        date = TODAY - relativedelta(months=int(splitted[0]))
        return str(date.isoformat())
    elif splitted[1].lower() in ['yrs', 'yr', 'years', 'year', 'y']:
        date = TODAY - relativedelta(years=int(splitted[0]))
        return str(date.isoformat())
    else:
        return "Wrong Argument format"

You can then call the function like this:

print get_past_date('5 hours ago')
print get_past_date('yesterday')
print get_past_date('3 days ago')
print get_past_date('4 months ago')
print get_past_date('2 years ago')
print get_past_date('today')

回答3:

Below code should work

from datetime import datetime, timedelta

N_DAYS_AGO = 5

today = datetime.now()    
n_days_ago = today - timedelta(days=N_DAYS_AGO)
print today, n_days_ago

来源：https://stackoverflow.com/questions/28268818/how-to-find-the-date-n-days-ago-in-python

标签

python-2.7

date

datetime

timedelta