5.5. Datetime Format

• format(dt, '%Y-%m-%d')

• f'Today is {dt:%Y-%m-%d}'

• dt.strftime('%Y-%m-%d')

5.5.1. 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'

5.5.2. 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 5.2. 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

5.5.3. 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

5.5.4. 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

5.5.5. References

[1]

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

5.5.6. Assignments

Code 5.16. Solution

"""
* Assignment: Datetime Format ISO-8601
* Complexity: easy
* Lines of code: 1 lines
* Time: 3 min

English:
    1. Define `result: str` with `DATA` in ISO-8601 format
    2. Do not use `datetime.isoformat()` method
    2. Run doctests - all must succeed

Polish:
    1. Zdefiniuj `result: str` z `DATA` w formacie ISO-8601
    2. Nie używaj metody `datetime.isoformat()`
    3. 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
    '1969-07-21 02:56:15'
"""

from datetime import datetime


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

# DATA in ISO-8601 format: '1969-07-21 02:56:15'
# type: str
result = ...

Code 5.17. 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
    >>> from pathlib import Path
    >>> content = Path(__file__).read_text()

    >>> assert '%'+'-H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'_H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'#H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'I' in content, \
    'Use %I for 12-hour clock'
    >>> assert '%'+'p' in content, \
    'Use %p for AM/PM'

    >>> 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 5.18. 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
    >>> from pathlib import Path
    >>> content = Path(__file__).read_text()

    >>> assert '%'+'-H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'_H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'#H' not in content, \
    '%H is used for 24-hour clock, use %I instead'
    >>> assert '%'+'-I' in content or '%'+'_I' in content, \
    'Use %I for 12-hour clock'
    >>> assert '%'+'p' in content, \
    'Use %p for AM/PM'

    >>> 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 = ...