Creating a range of dates in Python

Question

I want to create a list of dates, starting with today, and going back an arbitrary number of days, say, in my example 100 days. Is there a better way to do it than this?

import datetime

a = datetime.datetime.today()
numdays = 100
dateList = []
for x in range (0, numdays):
    dateList.append(a - datetime.timedelta(days = x))
print dateList

Answer 1

Pandas is great for time series in general, and has direct support for date ranges.

For example pd.date_range():

import pandas as pd
from datetime import datetime

datelist = pd.date_range(datetime.today(), periods=100).tolist()

It also has lots of options to make life easier. For example if you only wanted weekdays, you would just swap in bdate_range.

See date range documentation

In addition it fully supports pytz timezones and can smoothly span spring/autumn DST shifts.

EDIT by OP:

If you need actual python datetimes, as opposed to Pandas timestamps:

import pandas as pd
from datetime import datetime

pd.date_range(end = datetime.today(), periods = 100).to_pydatetime().tolist()

#OR

pd.date_range(start="2018-09-09",end="2020-02-02")

This uses the "end" parameter to match the original question, but if you want descending dates:

pd.date_range(datetime.today(), periods=100).to_pydatetime().tolist()

Answer 2

I wrote/maintain a package on pypi called dateroll specifically for this purpose.

It uses what we call "date schedule strings".

This can be accomplished in dateroll via the following:

pip install dateroll

>>> from dateroll import ddh #  date duration helper
>>> ddh("t-100d,t,1d").list
[Date(2024,1,6), Date(2024,1,7), Date(2024,1,8),...]

The function ddh takes a special string with 3 parts: a starting date, a stopping date, and an incremental date.

The dateroll.Date class inherits from datetime.Date so you can use them normally, or they have a property .date and .datetime to cast into python standard datetime.date and datetime.datetime

More complex examples in the docs:

https://dateroll.disent.com/docs/Quickstart

Answer 3

If using an external dependency is OK, check https://pypi.org/project/python-dateutil and its rrule module: https://dateutil.readthedocs.io/en/stable/rrule.html.

from dateutil import rrule
from datetime import datetime

list(rrule.rrule(rrule.DAILY,count=100,dtstart=datetime.now()))

Answer 4

From the title of this question I was expecting to find something like range(), that would let me specify two dates and create a list with all the dates in between. That way one does not need to calculate the number of days between those two dates, if one does not know it beforehand.

So with the risk of being slightly off-topic, this one-liner does the job:

import datetime
start_date = datetime.date(2011, 1, 1)
end_date   = datetime.date(2014, 1, 1)

dates_2011_2013 = [ start_date + datetime.timedelta(n) for n in range(int ((end_date - start_date).days))]

All credits to this answer!

Answer 5

from datetime import datetime , timedelta, timezone


start_date = '2022_01_25'
end_date = '2022_01_30'

start = datetime.strptime(start_date, "%Y_%m_%d")
print(type(start))
end =  datetime.strptime(end_date, "%Y_%m_%d")
##pDate = str(pDate).replace('-', '_')
number_of_days = (end - start).days

print("number_of_days: ", number_of_days)

##
date_list = []
for day in range(number_of_days):
    a_date = (start + timedelta(days = day)).astimezone(timezone.utc)
    a_date = a_date.strftime('%Y-%m-%d')
    date_list.append(a_date)

print(date_list)

Answer 6

A generic method that allows to create date ranges on parameterised window size(day, minute, hour, seconds):

from datetime import datetime, timedelta

def create_date_ranges(start, end, **interval):
    start_ = start
    while start_ < end:
        end_ = start_ + timedelta(**interval)
        yield (start_, min(end_, end))
        start_ = end_

Tests:

def main():
    tests = [
        ('2021-11-15:00:00:00', '2021-11-17:13:00:00', {'days': 1}),
        ('2021-11-15:00:00:00', '2021-11-16:13:00:00', {'hours': 12}),
        ('2021-11-15:00:00:00', '2021-11-15:01:45:00', {'minutes': 30}),
        ('2021-11-15:00:00:00', '2021-11-15:00:01:12', {'seconds': 30})
    ]
    for t in tests:
        print("\nInterval: %s, range(%s to %s)" % (t[2], t[0], t[1]))
        start = datetime.strptime(t[0], '%Y-%m-%d:%H:%M:%S')
        end =  datetime.strptime(t[1], '%Y-%m-%d:%H:%M:%S')
        ranges = list(create_date_ranges(start, end, **t[2]))        
        x = list(map(
            lambda x: (x[0].strftime('%Y-%m-%d:%H:%M:%S'), x[1].strftime('%Y-%m-%d:%H:%M:%S')),
            ranges
        ))
        print(x)
main()

Test output:

Interval: {'days': 1}, range(2021-11-15:00:00:00 to 2021-11-17:13:00:00)
[('2021-11-15:00:00:00', '2021-11-16:00:00:00'), ('2021-11-16:00:00:00', '2021-11-17:00:00:00'), ('2021-11-17:00:00:00', '2021-11-17:13:00:00')]

Interval: {'hours': 12}, range(2021-11-15:00:00:00 to 2021-11-16:13:00:00)
[('2021-11-15:00:00:00', '2021-11-15:12:00:00'), ('2021-11-15:12:00:00', '2021-11-16:00:00:00'), ('2021-11-16:00:00:00', '2021-11-16:12:00:00'), ('2021-11-16:12:00:00', '2021-11-16:13:00:00')]

Interval: {'minutes': 30}, range(2021-11-15:00:00:00 to 2021-11-15:01:45:00)
[('2021-11-15:00:00:00', '2021-11-15:00:30:00'), ('2021-11-15:00:30:00', '2021-11-15:01:00:00'), ('2021-11-15:01:00:00', '2021-11-15:01:30:00'), ('2021-11-15:01:30:00', '2021-11-15:01:45:00')]

Interval: {'seconds': 30}, range(2021-11-15:00:00:00 to 2021-11-15:00:01:12)
[('2021-11-15:00:00:00', '2021-11-15:00:00:30'), ('2021-11-15:00:00:30', '2021-11-15:00:01:00'), ('2021-11-15:00:01:00', '2021-11-15:00:01:12')]

Answer 7

I thought I'd throw in my two cents with a simple (and not complete) implementation of a date range:

from datetime import date, timedelta, datetime

class DateRange:
    def __init__(self, start, end, step=timedelta(1)):
        self.start = start
        self.end = end
        self.step = step

    def __iter__(self):
        start = self.start
        step = self.step
        end = self.end

        n = int((end - start) / step)
        d = start

        for _ in range(n):
            yield d
            d += step

    def __contains__(self, value):
        return (
            (self.start <= value < self.end) and 
            ((value - self.start) % self.step == timedelta(0))
        )

Answer 8

Another example that counts forwards or backwards, starting from Sandeep's answer.

from datetime import date, datetime, timedelta
from typing import Sequence
def range_of_dates(start_of_range: date, end_of_range: date) -> Sequence[date]:

    if start_of_range <= end_of_range:
        return [
            start_of_range + timedelta(days=x)
            for x in range(0, (end_of_range - start_of_range).days + 1)
        ]
    return [
        start_of_range - timedelta(days=x)
        for x in range(0, (start_of_range - end_of_range).days + 1)
    ]

start_of_range = datetime.today().date()
end_of_range = start_of_range + timedelta(days=3)
date_range = range_of_dates(start_of_range, end_of_range)
print(date_range)

gives

[datetime.date(2019, 12, 20), datetime.date(2019, 12, 21), datetime.date(2019, 12, 22), datetime.date(2019, 12, 23)]

and

start_of_range = datetime.today().date()
end_of_range = start_of_range - timedelta(days=3)
date_range = range_of_dates(start_of_range, end_of_range)
print(date_range)

gives

[datetime.date(2019, 12, 20), datetime.date(2019, 12, 19), datetime.date(2019, 12, 18), datetime.date(2019, 12, 17)]

Note that the start date is included in the return, so if you want four total dates, use timedelta(days=3)

Answer 9

From above answers i created this example for date generator

import datetime
date = datetime.datetime.now()
time = date.time()
def date_generator(date, delta):
  counter =0
  date = date - datetime.timedelta(days=delta)
  while counter <= delta:
    yield date
    date = date + datetime.timedelta(days=1)
    counter +=1

for date in date_generator(date, 30):
   if date.date() != datetime.datetime.now().date():
     start_date = datetime.datetime.combine(date, datetime.time())
     end_date = datetime.datetime.combine(date, datetime.time.max)
   else:
     start_date = datetime.datetime.combine(date, datetime.time())
     end_date = datetime.datetime.combine(date, time)
   print('start_date---->',start_date,'end_date---->',end_date)

Answer 10

Marginally better...

base = datetime.datetime.today()
date_list = [base - datetime.timedelta(days=x) for x in range(numdays)]

Answer 11

A monthly date range generator with datetime and dateutil. Simple and easy to understand:

import datetime as dt
from dateutil.relativedelta import relativedelta

def month_range(start_date, n_months):
        for m in range(n_months):
            yield start_date + relativedelta(months=+m)

Answer 12

If there are two dates and you need the range try

from dateutil import rrule, parser
date1 = '1995-01-01'
date2 = '1995-02-28'
datesx = list(rrule.rrule(rrule.DAILY, dtstart=parser.parse(date1), until=parser.parse(date2)))

Answer 13

I know this has been answered, but I'll put down my answer for historical purposes, and since I think it is straight forward.

import numpy as np
import datetime as dt
listOfDates=[date for date in np.arange(firstDate,lastDate,dt.timedelta(days=x))]

Sure it won't win anything like code-golf, but I think it is elegant.

Answer 14

Based on answers I wrote for myself this:

import datetime;
print [(datetime.date.today() - datetime.timedelta(days=x)).strftime('%Y-%m-%d') for x in range(-5, 0)]

Output:

['2017-12-11', '2017-12-10', '2017-12-09', '2017-12-08', '2017-12-07']

The difference is that I get the 'date' object, not the 'datetime.datetime' one.

Answer 15

Here's a slightly different answer building off of S.Lott's answer that gives a list of dates between two dates start and end. In the example below, from the start of 2017 to today.

start = datetime.datetime(2017,1,1)
end = datetime.datetime.today()
daterange = [start + datetime.timedelta(days=x) for x in range(0, (end-start).days)]

Answer 16

You can also use the day ordinal to make it simpler:

def date_range(start_date, end_date):
    for ordinal in range(start_date.toordinal(), end_date.toordinal()):
        yield datetime.date.fromordinal(ordinal)

Or as suggested in the comments you can create a list like this:

date_range = [
    datetime.date.fromordinal(ordinal) 
    for ordinal in range(
        start_date.toordinal(),
        end_date.toordinal(),
    )
]

Answer 17

from datetime import datetime, timedelta
from dateutil import parser
def getDateRange(begin, end):
    """  """
    beginDate = parser.parse(begin)
    endDate =  parser.parse(end)
    delta = endDate-beginDate
    numdays = delta.days + 1
    dayList = [datetime.strftime(beginDate + timedelta(days=x), '%Y%m%d') for x in range(0, numdays)]
    return dayList

Answer 18

Here's a one liner for bash scripts to get a list of weekdays, this is python 3. Easily modified for whatever, the int at the end is the number of days in the past you want.

python -c "import sys,datetime; print('\n'.join([(datetime.datetime.today() - datetime.timedelta(days=x)).strftime(\"%Y/%m/%d\") for x in range(0,int(sys.argv[1])) if (datetime.datetime.today() - datetime.timedelta(days=x)).isoweekday()<6]))" 10

Here is a variant to provide a start (or rather, end) date

python -c "import sys,datetime; print('\n'.join([(datetime.datetime.strptime(sys.argv[1],\"%Y/%m/%d\") - datetime.timedelta(days=x)).strftime(\"%Y/%m/%d \") for x in range(0,int(sys.argv[2])) if (datetime.datetime.today() - datetime.timedelta(days=x)).isoweekday()<6]))" 2015/12/30 10

Here is a variant for arbitrary start and end dates. not that this isn't terribly efficient, but is good for putting in a for loop in a bash script:

python -c "import sys,datetime; print('\n'.join([(datetime.datetime.strptime(sys.argv[1],\"%Y/%m/%d\") + datetime.timedelta(days=x)).strftime(\"%Y/%m/%d\") for x in range(0,int((datetime.datetime.strptime(sys.argv[2], \"%Y/%m/%d\") - datetime.datetime.strptime(sys.argv[1], \"%Y/%m/%d\")).days)) if (datetime.datetime.strptime(sys.argv[1], \"%Y/%m/%d\") + datetime.timedelta(days=x)).isoweekday()<6]))" 2015/12/15 2015/12/30

Answer 19

import datetime    
def date_generator():
    cur = base = datetime.date.today()
    end  = base + datetime.timedelta(days=100)
    delta = datetime.timedelta(days=1)
    while(end>base):
        base = base+delta
        print base

date_generator()

Answer 20

Matplotlib related

from matplotlib.dates import drange
import datetime

base = datetime.date.today()
end  = base + datetime.timedelta(days=100)
delta = datetime.timedelta(days=1)
l = drange(base, end, delta)

Answer 21

Get range of dates between specified start and end date (Optimized for time & space complexity):

import datetime

start = datetime.datetime.strptime("21-06-2014", "%d-%m-%Y")
end = datetime.datetime.strptime("07-07-2014", "%d-%m-%Y")
date_generated = [start + datetime.timedelta(days=x) for x in range(0, (end-start).days)]

for date in date_generated:
    print date.strftime("%d-%m-%Y")

Answer 22

Here is gist I created, from my own code, this might help. (I know the question is too old, but others can use it)

https://gist.github.com/2287345

(same thing below)

import datetime
from time import mktime

def convert_date_to_datetime(date_object):
    date_tuple = date_object.timetuple()
    date_timestamp = mktime(date_tuple)
    return datetime.datetime.fromtimestamp(date_timestamp)

def date_range(how_many=7):
    for x in range(0, how_many):
        some_date = datetime.datetime.today() - datetime.timedelta(days=x)
        some_datetime = convert_date_to_datetime(some_date.date())
        yield some_datetime

def pick_two_dates(how_many=7):
    a = b = convert_date_to_datetime(datetime.datetime.now().date())
    for each_date in date_range(how_many):
        b = a
        a = each_date
        if a == b:
            continue
        yield b, a

Answer 23

A bit of a late answer I know, but I just had the same problem and decided that Python's internal range function was a bit lacking in this respect so I've overridden it in a util module of mine.

from __builtin__ import range as _range
from datetime import datetime, timedelta

def range(*args):
    if len(args) != 3:
        return _range(*args)
    start, stop, step = args
    if start < stop:
        cmp = lambda a, b: a < b
        inc = lambda a: a + step
    else:
        cmp = lambda a, b: a > b
        inc = lambda a: a - step
    output = [start]
    while cmp(start, stop):
        start = inc(start)
        output.append(start)

    return output

print range(datetime(2011, 5, 1), datetime(2011, 10, 1), timedelta(days=30))

Answer 24

You can write a generator function that returns date objects starting from today:

import datetime

def date_generator():
  from_date = datetime.datetime.today()
  while True:
    yield from_date
    from_date = from_date - datetime.timedelta(days=1)

This generator returns dates starting from today and going backwards one day at a time. Here is how to take the first 3 dates:

>>> import itertools
>>> dates = itertools.islice(date_generator(), 3)
>>> list(dates)
[datetime.datetime(2009, 6, 14, 19, 12, 21, 703890), datetime.datetime(2009, 6, 13, 19, 12, 21, 703890), datetime.datetime(2009, 6, 12, 19, 12, 21, 703890)]

The advantage of this approach over a loop or list comprehension is that you can go back as many times as you want.

Edit

A more compact version using a generator expression instead of a function:

date_generator = (datetime.datetime.today() - datetime.timedelta(days=i) for i in itertools.count())

Usage:

>>> dates = itertools.islice(date_generator, 3)
>>> list(dates)
[datetime.datetime(2009, 6, 15, 1, 32, 37, 286765), datetime.datetime(2009, 6, 14, 1, 32, 37, 286836), datetime.datetime(2009, 6, 13, 1, 32, 37, 286859)]