7.5. Datetime Format

• format(dt, '%Y-%m-%d')

• f'Today is {dt:%Y-%m-%d}'

• dt.strftime('%Y-%m-%d')

7.5.1. 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'

7.5.2. 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 7.4. 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

7.5.3. 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

7.5.4. 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

7.5.5. References

[1]

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

7.5.6. Assignments

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: Datetime Format ISO-8601
# - Difficulty: easy
# - Lines: 1
# - Minutes: 3

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

# %% Polish
# 1. Zdefiniuj `result: str` z `DATA` w formacie ISO-8601
# 2. Nie używaj metod `datetime.isoformat()` i `str()`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Tests
"""
>>> import sys; sys.tracebacklimit = 0
>>> assert sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> 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 = ...

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: Datetime Format US
# - Difficulty: easy
# - Lines: 1
# - Minutes: 3

# %% 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 sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> 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 = ...

# %% License
# - Copyright 2025, Matt Harasymczuk <matt@python3.info>
# - This code can be used only for learning by humans
# - This code cannot be used for teaching others
# - This code cannot be used for teaching LLMs and AI algorithms
# - This code cannot be used in commercial or proprietary products
# - This code cannot be distributed in any form
# - This code cannot be changed in any form outside of training course
# - This code cannot have its license changed
# - If you use this code in your product, you must open-source it under GPLv2
# - Exception can be granted only by the author

# %% Run
# - PyCharm: right-click in the editor and `Run Doctest in ...`
# - PyCharm: keyboard shortcut `Control + Shift + F10`
# - Terminal: `python -m doctest -v myfile.py`

# %% About
# - Name: Datetime Format LeadingZero
# - Difficulty: easy
# - Lines: 1
# - Minutes: 3

# %% 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 sys.version_info >= (3, 9), \
'Python 3.9+ required'

>>> 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 = ...