Format a datetime into a string with milliseconds

Question

How can I format a datetime object as a string with milliseconds?

Answer 1

To get a date string with milliseconds, use [:-3] to trim the last three digits of %f (microseconds):

>>> from datetime import datetime
>>> datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S.%f')[:-3]
'2022-09-24 10:18:32.926'

Or shorter:

>>> from datetime import datetime
>>> datetime.utcnow().strftime('%F %T.%f')[:-3]
'2022-09-24 10:18:32.926'

See the Python docs for more "%" format codes and the strftime(3) man page for the full list.

Answer 2

With Python 3.6+, you can set isoformat's timespec:

>>> from datetime import datetime
>>> datetime.utcnow().isoformat(sep=' ', timespec='milliseconds')
'2019-05-10 09:08:53.155'

Answer 3

@Cabbi raised the issue that on some systems (Windows with Python 2.7), the microseconds format %f may incorrectly give "0", so it's not portable to simply trim the last three characters. Such systems do not follow the behavior specified by the documentation:

Directive	Meaning	Example
%f	Microsecond as a decimal number, zero-padded to 6 digits.	000000, 000001, …, 999999

The following code carefully formats a timestamp with milliseconds:

>>> from datetime import datetime
>>> (dt, micro) = datetime.utcnow().strftime('%Y-%m-%d %H:%M:%S.%f').split('.')
>>> "%s.%03d" % (dt, int(micro) / 1000)
'2016-02-26 04:37:53.133'

To get the exact output that the OP wanted, we have to strip punctuation characters:

>>> from datetime import datetime
>>> (dt, micro) = datetime.utcnow().strftime('%Y%m%d%H%M%S.%f').split('.')
>>> "%s%03d" % (dt, int(micro) / 1000)
'20160226043839901'

Answer 4

Using strftime:

>>> from datetime import datetime
>>> datetime.utcnow().strftime('%Y%m%d%H%M%S%f')
'20220402055654344968'

Answer 5

Use [:-3] to remove the 3 last characters since %f is for microseconds:

>>> from datetime import datetime
>>> datetime.now().strftime('%Y/%m/%d %H:%M:%S.%f')[:-3]
'2013/12/04 16:50:03.141'

Answer 6

In python 3.6 and above using python f-strings:

from datetime import datetime, timezone

dt = datetime.now(timezone.utc)

print(f"{dt:%Y-%m-%d %H:%M:%S}.{dt.microsecond // 1000:03d}")

The code specific to format milliseconds is:

{dt.microsecond // 1000:03d}

The format string {:03d} and microsecond to millisecond conversion // 1000 is from def _format_time in https://github.com/python/cpython/blob/master/Lib/datetime.py that is used for datetime.datetime.isoformat().

Answer 7

import datetime

# convert string into date time format.

str_date = '2016-10-06 15:14:54.322989'
d_date = datetime.datetime.strptime(str_date , '%Y-%m-%d %H:%M:%S.%f')
print(d_date)
print(type(d_date)) # check d_date type.


# convert date time to regular format.

reg_format_date = d_date.strftime("%d %B %Y %I:%M:%S %p")
print(reg_format_date)

# some other date formats.
reg_format_date = d_date.strftime("%Y-%m-%d %I:%M:%S %p")
print(reg_format_date)
reg_format_date = d_date.strftime("%Y-%m-%d %H:%M:%S")
print(reg_format_date)

<<<<<< OUTPUT >>>>>>>

2016-10-06 15:14:54.322989    
<class 'datetime.datetime'>    
06 October 2016 03:14:54 PM    
2016-10-06 03:14:54 PM    
2016-10-06 15:14:54

Answer 8

I assume you mean you're looking for something that is faster than datetime.datetime.strftime(), and are essentially stripping the non-alpha characters from a utc timestamp.

You're approach is marginally faster, and I think you can speed things up even more by slicing the string:

>>> import timeit
>>> t=timeit.Timer('datetime.utcnow().strftime("%Y%m%d%H%M%S%f")','''
... from datetime import datetime''')
>>> t.timeit(number=10000000)
116.15451288223267

>>> def replaceutc(s):
...     return s\
...         .replace('-','') \
...         .replace(':','') \
...         .replace('.','') \
...         .replace(' ','') \
...         .strip()
... 
>>> t=timeit.Timer('replaceutc(str(datetime.datetime.utcnow()))','''
... from __main__ import replaceutc
... import datetime''')
>>> t.timeit(number=10000000)
77.96774983406067

>>> def sliceutc(s):
...     return s[:4] + s[5:7] + s[8:10] + s[11:13] + s[14:16] + s[17:19] + s[20:]
... 
>>> t=timeit.Timer('sliceutc(str(datetime.utcnow()))','''
... from __main__ import sliceutc
... from datetime import datetime''')
>>> t.timeit(number=10000000)
62.378515005111694

Answer 9

In Python 3.11 (maybe older version support it too) it can be done with isoformat(timespec='milliseconds')

From datetime.py:

The optional argument timespec specifies the number of additional terms of the time to include. Valid options are 'auto', 'hours', 'minutes', 'seconds', 'milliseconds' and 'microseconds'.

>>> datetime.now().isoformat(timespec='milliseconds')
'2023-12-01T10:34:18.657'

Answer 10

from datetime import datetime
from time import clock

t = datetime.utcnow()
print 't == %s    %s\n\n' % (t,type(t))

n = 100000

te = clock()
for i in xrange(1):
    t_stripped = t.strftime('%Y%m%d%H%M%S%f')
print clock()-te
print t_stripped," t.strftime('%Y%m%d%H%M%S%f')"

print

te = clock()
for i in xrange(1):
    t_stripped = str(t).replace('-','').replace(':','').replace('.','').replace(' ','')
print clock()-te
print t_stripped," str(t).replace('-','').replace(':','').replace('.','').replace(' ','')"

print

te = clock()
for i in xrange(n):
    t_stripped = str(t).translate(None,' -:.')
print clock()-te
print t_stripped," str(t).translate(None,' -:.')"

print

te = clock()
for i in xrange(n):
    s = str(t)
    t_stripped = s[:4] + s[5:7] + s[8:10] + s[11:13] + s[14:16] + s[17:19] + s[20:] 
print clock()-te
print t_stripped," s[:4] + s[5:7] + s[8:10] + s[11:13] + s[14:16] + s[17:19] + s[20:] "

result

t == 2011-09-28 21:31:45.562000    <type 'datetime.datetime'>


3.33410112179
20110928212155046000  t.strftime('%Y%m%d%H%M%S%f')

1.17067364707
20110928212130453000 str(t).replace('-','').replace(':','').replace('.','').replace(' ','')

0.658806915404
20110928212130453000 str(t).translate(None,' -:.')

0.645189262881
20110928212130453000 s[:4] + s[5:7] + s[8:10] + s[11:13] + s[14:16] + s[17:19] + s[20:]

Use of translate() and slicing method run in same time
translate() presents the advantage to be usable in one line

Comparing the times on the basis of the first one:

1.000 * t.strftime('%Y%m%d%H%M%S%f')

0.351 * str(t).replace('-','').replace(':','').replace('.','').replace(' ','')

0.198 * str(t).translate(None,' -:.')

0.194 * s[:4] + s[5:7] + s[8:10] + s[11:13] + s[14:16] + s[17:19] + s[20:]

Answer 11

I dealt with the same problem but in my case it was important that the millisecond was rounded and not truncated

from datetime import datetime, timedelta

def strftime_ms(datetime_obj):
    y,m,d,H,M,S = datetime_obj.timetuple()[:6]
    ms = timedelta(microseconds = round(datetime_obj.microsecond/1000.0)*1000)
    ms_date = datetime(y,m,d,H,M,S) + ms
    return ms_date.strftime('%Y-%m-%d %H:%M:%S.%f')[:-3]

Answer 12

python -c "from datetime import datetime; print str(datetime.now())[:-3]"
2017-02-09 10:06:37.006

Answer 13

datetime
t = datetime.datetime.now()
ms = '%s.%i' % (t.strftime('%H:%M:%S'), t.microsecond/1000)
print(ms)
14:44:37.134

Answer 14

If you are prepared to store the time in a variable and do a little string manipulation, then you can actually do this without using the datetime module.

>>> _now = time.time()
>>> print ("Time : %s.%s\n" % (time.strftime('%x %X',time.localtime(_now)),
... str('%.3f'%_now).split('.')[1])) # Rounds to nearest millisecond
Time : 05/02/21 01:16:58.676

>>> 

%.3f will round to out put the nearest millisecond, if you want more or less precision just change the number of decimal places

>>> print ("Time : %s.%s\n" % (time.strftime('%x %X',time.localtime(_now)),
... str('%.1f'%_now).split('.')[1])) # Rounds to nearest tenth of a second
Time : 05/02/21 01:16:58.7

>>>

Tested in Python 2.7 and 3.7 (obviously you need to leave out the brackets when calling print in version 2.x).

Answer 15

The problem with datetime.utcnow() and other such solutions is that they are slow.

More efficient solution may look like this one:

def _timestamp(prec=0):
    t = time.time()
    s = time.strftime("%H:%M:%S", time.localtime(t))
    if prec > 0:
        s += ("%.9f" % (t % 1,))[1:2+prec]
    return s

Where prec would be 3 in your case (milliseconds).

The function works up to 9 decimal places (please note number 9 in the 2nd formatting string).

If you'd like to round the fractional part, I'd suggest building "%.9f" dynamically with desired number of decimal places.

Answer 16

Field-width format specification

The UNIX date command allows specifying %3 to reduce the precision to 3 digits:

$ date '+%Y-%m-%d %H:%M:%S.%3N'
2022-01-01 00:01:23.456

Here's a custom function that can do that in Python:

from datetime import datetime

def strftime_(fmt: str, dt: datetime) -> str:
    tokens = fmt.split("%")
    tokens[1:] = [_format_token(dt, x) for x in tokens[1:]]
    return "".join(tokens)

def _format_token(dt: datetime, token: str) -> str:
    if len(token) == 0:
        return ""
    if token[0].isnumeric():
        width = int(token[0])
        s = dt.strftime(f"%{token[1]}")[:width]
        return f"{s}{token[2:]}"
    return dt.strftime(f"%{token}")

Example usage:

>>> strftime_("%Y-%m-%d %H:%M:%S.%3f", datetime.now())
'2022-01-01 00:01:23.456'

NOTE: %% is not supported.

Answer 17

It depends on how whether you want to truncate or round microseconds:

• example time:

  tm = time(10,11,12,microsecond=95900)

• truncating - as others have mentioned above:

  print(f'{tm:%H:%M:%S.%f}'[:-3])

  10:11:12.095

• rounding - AFAIK there is no format specifier in Python to do this so you have to round the microseconds then format:

  print(f'{tm:%H:%M:%S}.{tm.microsecond/1000:03.0f}')

  10:11:12.096