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Convert string date to timestamp in Python

Posted by: admin November 1, 2017 Leave a comment

Questions:

How to convert a string in the format "%d/%m/%Y" to timestamp?

"01/12/2011" -> 1322697600
Answers:
>>> import time
>>> import datetime
>>> s = "01/12/2011"
>>> time.mktime(datetime.datetime.strptime(s, "%d/%m/%Y").timetuple())
1322697600.0

Questions:
Answers:

To convert the string into a date object:

from datetime import date, datetime

date_string = "01/12/2011"
date_object = date(*map(int, reversed(date_string.split("/"))))
assert date_object == datetime.strptime(date_string, "%d/%m/%Y").date()

The way to convert the date object into POSIX timestamp depends on timezone. From Converting datetime.date to UTC timestamp in Python:

  • date object represents midnight in UTC

    import calendar
    
    timestamp1 = calendar.timegm(utc_date.timetuple())
    timestamp2 = (utc_date.toordinal() - date(1970, 1, 1).toordinal()) * 24*60*60
    assert timestamp1 == timestamp2
    
  • date object represents midnight in local time

    import time
    
    timestamp3 = time.mktime(local_date.timetuple())
    assert timestamp3 != timestamp1 or (time.gmtime() == time.localtime())
    

The timestamps are different unless midnight in UTC and in local time is the same time instance.

Questions:
Answers:
>>> int(datetime.datetime.strptime('01/12/2011', '%d/%m/%Y').strftime("%s"))
1322683200

Questions:
Answers:

i use ciso8601 which is 62x faster than datetime’s strptime.

t = "01/12/2011"
ts = ciso8601.parse_datetime(t)
# to get time in seconds:
time.mktime(ts.timetuple())

you can learn more at here

Questions:
Answers:

The answer depends also on your input date timezone. If your date is a local date, then you can use mktime() like katrielalex said – only I don’t see why he used datetime instead of this shorter version:

>>> time.mktime(time.strptime('01/12/2011', "%d/%m/%Y"))
1322694000.0

But observe that my result is different than his, as I am probably in a different TZ (and the result is timezone-free UNIX timestamp)

Now if the input date is already in UTC, than I believe the right solution is:

>>> calendar.timegm(time.strptime('01/12/2011', '%d/%m/%Y'))
1322697600

Questions:
Answers:

First you must the strptime class to convert the string to a struct_time format.

Then just use mktime from there to get your float.

Questions:
Answers:

I would suggest dateutil:

import dateutil.parser
dateutil.parser.parse("01/12/2011", dayfirst=True).timestamp()

Questions:
Answers:

A lot of these answers don’t bother to consider that the date is naive to begin with

To be correct, you need to make the naive date a timezone aware datetime first

import datetime
import pytz
# naive datetime
d = datetime.datetime.strptime('01/12/2011', '%d/%m/%Y')
>>> datetime.datetime(2011, 12, 1, 0, 0)

# add proper timezone
pst = pytz.timezone('America/Los_Angeles')
d = pst.localize(d)
>>> datetime.datetime(2011, 12, 1, 0, 0,
tzinfo=<DstTzInfo 'America/Los_Angeles' PST-1 day, 16:00:00 STD>)

# convert to UTC timezone
utc = pytz.UTC
d = d.astimezone(utc)
>>> datetime.datetime(2011, 12, 1, 8, 0, tzinfo=<UTC>)

# epoch is the beginning of time in the UTC timestamp world
epoch = datetime.datetime(1970,1,1,0,0,0,tzinfo=pytz.UTC)
>>> datetime.datetime(1970, 1, 1, 0, 0, tzinfo=<UTC>)

# get the total second difference
ts = (d - epoch).total_seconds()
>>> 1322726400.0

Also:

Be careful, using pytz for tzinfo in a datetime.datetime DOESN’T WORK for many timezones. See datetime with pytz timezone. Different offset depending on how tzinfo is set

# Don't do this:
d = datetime.datetime(2011, 12, 1,0,0,0, tzinfo=pytz.timezone('America/Los_Angeles'))
>>> datetime.datetime(2011, 1, 12, 0, 0, 
tzinfo=<DstTzInfo 'America/Los_Angeles' LMT-1 day, 16:07:00 STD>)
# tzinfo in not PST but LMT here, with a 7min offset !!!

# when converting to UTC:
d = d.astimezone(pytz.UTC)
>>> datetime.datetime(2011, 1, 12, 7, 53, tzinfo=<UTC>)
# you end up with an offset

https://en.wikipedia.org/wiki/Local_mean_time

Questions:
Answers:

just use datetime.timestamp(your datetime instanse), datetime instance contains the timezone infomation, so the timestamp will be a standard utc timestamp. if you transform the datetime to timetuple, it will lose it’s timezone, so the result will be error.
if you want to provide an interface, you should write like this:
int(datetime.timestamp(time_instance)) * 1000