11.4. Datetime Format

• format(dt, '%Y-%m-%d')

• f'Today is {dt:%Y-%m-%d}'

• dt.strftime('%Y-%m-%d')

11.4.1. Formats

• format(dt, '%Y-%m-%d')

>>> from datetime import datetime
>>>
>>>
>>> dt = datetime(1961, 4, 12, 6, 7)
>>>
>>> format(dt, '%Y')
'1961'
>>>
>>> format(dt, '%Y-%m-%d')
'1961-04-12'
>>>
>>> format(dt, '%d.%m.%Y')
'12.04.1961'
>>>
>>> format(dt, '%H:%M')
'06:07'
>>>
>>> format(dt, '%Y-%m-%d %H:%M')
'1961-04-12 06:07'
>>>
>>> format(dt, '%Y-%m-%d %H:%M:%S')
'1961-04-12 06:07:00'
>>>
>>> format(dt, '%B %d, %Y')
'April 12, 1961'

11.4.2. Parameters

• Similar in almost all programming language

• Some minor differences like in JavaScript minutes are i, not M

Table 11.1. Date and time parsing and formatting parameters

Directive	Example	Meaning
%a	Sun, Mon, ..., Sat	Weekday as locale's abbreviated name
%A	Sunday, Monday, ..., Saturday (en_US)	Weekday as locale's full name
%w	0, 1, ..., 6	Weekday as a decimal number, where 0 is Sunday and 6 is Saturday
%d	01, 02, ..., 31	Day of the month as a zero-padded decimal number
%b	Jan, Feb, ..., Dec (en_US)	Month as locale's abbreviated name
%B	January, February, ..., December (en_US)	Month as locale's full name
%m	01, 02, ..., 12	Month as a zero-padded decimal number
%y	00, 01, ..., 99	Year without century as a zero-padded decimal number
%Y	0001, 0002, ..., 2013, 2014, ..., 9998, 9999	Year with century as a decimal number
%H	00, 01, ..., 23	Hour (24-hour clock) as a zero-padded decimal number
%I	01, 02, ..., 12	Hour (12-hour clock) as a zero-padded decimal number
%p	AM, PM (en_US)	Locale's equivalent of either AM or PM
%M	00, 01, ..., 59	Minute as a zero-padded decimal number
%S	00, 01, ..., 59	Second as a zero-padded decimal number
%f	000000, 000001, ..., 999999	Microsecond as a decimal number, zero-padded on the left
%z	(empty), +0000, -0400, +1030	UTC offset in the form +HHMM or -HHMM (empty string if the object is naive)
%Z	(empty), UTC, EST, CST	Time zone name (empty string if the object is naive)
%j	001, 002, ..., 366	Day of the year as a zero-padded decimal number
%U	00, 01, ..., 53	Week number of the year (Sunday as the first day of the week) as a zero padded decimal number. All days in a new year preceding the first Sunday are considered to be in week 0
%W	00, 01, ..., 53	Week number of the year (Monday as the first day of the week) as a decimal number. All days in a new year preceding the first Monday are considered to be in week 0
%c	Tue Aug 16 21:30:00 1988 (en_US)	Locale's appropriate date and time representation
%x	08/16/1988 (en_US); 16.08.1988 (de_DE)	Locale's appropriate date representation
%X	21:30:00	Locale's appropriate time representation
%%	%	A literal % character
%G	0001, 0002, ..., 2013, 2014, ..., 9998, 9999	ISO 8601 year with century representing the year that contains the greater part of the ISO week (%V)
%u	1, 2, ..., 7	ISO 8601 weekday as a decimal number where 1 is Monday
%V	01, 02, ..., 53	ISO 8601 week as a decimal number with Monday as the first day of the week. Week 01 is the week containing Jan 4

11.4.3. Leading Zero

• %#H - remove leading zero (Windows)

• %-H - remove leading zero (macOS, Linux, *nix)

• %_H - replace leading zero with space (macOS, Linux, *nix)

• Works only with formatting

• raises ValueError while parsing 1

On Linux and *nix systems:

>>> from datetime import datetime
>>>
>>>
>>> dt = datetime(1961, 4, 12, 6, 7)
>>>
>>> format(dt, '%H:%M')
'06:07'
>>>
>>> format(dt, '%-H:%M')
'6:07'
>>>
>>> format(dt, '%_H:%M')
' 6:07'
>>>
>>> format(dt, '%#H:%M')  
'06:07'

On macOS:

>>> from datetime import datetime
>>>
>>>
>>> dt = datetime(1961, 4, 12, 6, 7)
>>>
>>> format(dt, '%H:%M')
'06:07'
>>>
>>> format(dt, '%-H:%M')
'6:07'
>>>
>>> format(dt, '%#H:%M')  
'#H:07'

On Windows 10:

>>> from datetime import datetime
>>>
>>>
>>> dt = datetime(1961, 4, 12, 6, 7)
>>>
>>> format(dt, '%H:%M')
'06:07'
>>>
>>> format(dt, '%-H:%M')  
Traceback (most recent call last):
ValueError: Invalid format string
>>>
>>> format(dt, '%_H:%M')  
Traceback (most recent call last):
ValueError: Invalid format string
>>>
>>> format(dt, '%#H:%M')  
'6:07'

Table 11.2. Leading Zero

Meaning	With	Without (macOS, Linux)	Without (Windows)
day	%d	%-d	%#d
hour 24h	%H	%-H	%#H
hour 12h	%I	%-I	%#I
day of a year	%j	%-j	%#j
month	%m	%-m	%#m
minute	%M	%-M	%#M
second	%S	%-S	%#S
week number (Sunday first)	%U	%-U	%#U
week number (Monday first)	%W	%-W	%#W
weekday (Sunday first)	%w	%-w	%#w
year short	%y	%-y	%#y
year long	%Y	%-Y	%#Y

11.4.4. String Format Time

• datetime.strftime()

>>> from datetime import datetime
>>>
>>>
>>> gagarin = datetime(1961, 4, 12, 6, 7)
>>> formatted = gagarin.strftime('%Y-%m-%d %H:%M')
>>>
>>> print(f'Gagarin launched on {formatted}')
Gagarin launched on 1961-04-12 06:07

11.4.5. Format String

>>> from datetime import datetime
>>>
>>>
>>> gagarin = datetime(1961, 4, 12, 6, 7)
>>>
>>> print(f'Gagarin launched on {gagarin:%Y-%m-%d}')
Gagarin launched on 1961-04-12
>>>
>>> print(f'Gagarin launched on {gagarin:%Y-%m-%d %H:%M}')
Gagarin launched on 1961-04-12 06:07

>>> from datetime import datetime
>>>
>>>
>>> gagarin = datetime(1961, 4, 12, 6, 7)
>>> format = '%Y-%m-%d %H:%M'
>>>
>>> print(f'Gagarin launched on {gagarin:{format}}')
Gagarin launched on 1961-04-12 06:07

11.4.6. References

1

https://docs.python.org/3/library/datetime.html#strftime-and-strptime-behavior

11.4.7. Assignments

Code 11.29. Solution

"""
* Assignment: Datetime Format US
* Complexity: easy
* Lines of code: 1 lines
* Time: 3 min

English:
    1. Define `result: str` with `DATA` in long US format
    2. Run doctests - all must succeed

Polish:
    1. Zdefiniuj `result: str` z `DATA` w długim formacie amerykańskim
    2. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> assert type(result) is str, \
    'Variable `result` has invalid type, must be a str'

    >>> result
    'July 21, 1969 02:56:15 AM'
"""

from datetime import datetime


DATA = datetime(1969, 7, 21, 2, 56, 15)

# DATA in long US format: 'July 21, 1969 02:56:15 AM'
# type: str
result = ...

Code 11.30. Solution

"""
* Assignment: Datetime Format LeadingZero
* Complexity: easy
* Lines of code: 1 lines
* Time: 3 min

English:
    1. Define `result: str` with `DATA` in short US format
    2. Make sure, that month, day and hour are without leading zero
    3. Run doctests - all must succeed

Polish:
    1. Zdefiniuj `result: str` z `DATA` w krótkim formacie amerykańskim
    2. Upewnij się, że miesiąc, dzień i godzina jest bez wiodącego zera
    3. Uruchom doctesty - wszystkie muszą się powieść

Hints:
    * Use `%-I` on \*nix systems (macOS, BSD, Linux)
    * Use `%#I` on Windows

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> assert type(result) is str, \
    'Variable `result` has invalid type, must be a str'

    >>> result
    '7/21/69 2:56 AM'
"""

from datetime import datetime


DATA = datetime(1969, 7, 21, 2, 56, 15)

# DATA in short US format: '7/21/69 2:56 AM'
# type: str
result = ...