• format(dt, '%Y-%m-%d')

  • f'Today is {dt:%Y-%m-%d}'

  • dt.strftime('%Y-%m-%d')

8.8.1. 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'

8.8.2. 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 8.4. 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

8.8.3. 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

8.8.4. 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

8.8.5. References

8.8.6. Assignments

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

# %% 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

# %% English
# 1. Define `result: str` with `DATA` in ISO-8601 format
#    example: `1969-07-21 02:56:15`
# 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
#    przykład: `1969-07-21 02:56:15`
# 2. Nie używaj metod `datetime.isoformat()` i `str()`
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# '1969-07-21 02:56:15'

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

>>> result
'1969-07-21 02:56:15'
"""

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

# %% Imports
from datetime import datetime

# %% Types
result: str

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

# %% Result
result = ...


# TODO: nie działa w Jupyter Notebook (bo nie ma __file__)

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

# %% 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

# %% English
# 1. Define `result: str` with `DATA` in long US format
#    example: `July 21, 1969 02:56:15 AM`
# 2. Run doctests - all must succeed

# %% Polish
# 1. Zdefiniuj `result: str` z `DATA` w długim formacie amerykańskim
#    przykład: `July 21, 1969 02:56:15 AM`
# 2. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# 'July 21, 1969 02:56:15 AM'

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

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

>>> assert '%'+'-H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'_H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'#H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'I' in content, \
'Value `%I` was not used; use `%I` for 12-hour clock.'

>>> assert '%'+'p' in content, \
'Value `%p` was not used; use `%p` for AM/PM.'

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

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

# %% Imports
from datetime import datetime

# %% Types
result: str

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

# %% Result
result = ...


# TODO: nie działa w Jupyter Notebook (bo nie ma __file__)

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

# %% 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

# %% English
# 1. Define `result: str` with `DATA` in short US format
#    example: `7/21/69 2:56 AM`
# 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
#    przykład: `7/21/69 2:56 AM`
# 2. Upewnij się, że miesiąc, dzień i godzina jest bez wiodącego zera
# 3. Uruchom doctesty - wszystkie muszą się powieść

# %% Expected
# >>> result
# '7/21/69 2:56 AM'

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

# %% Doctests
"""
>>> import sys; sys.tracebacklimit = 0

>>> assert sys.version_info >= (3, 9), \
'Python has an is invalid version; expected: `3.9` or newer.'

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

>>> assert '%'+'-H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'_H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'#H' not in content, \
'Value `%H` was used; use `%I` for 12-hour clock.'

>>> assert '%'+'I' in content, \
'Value `%I` was not used; use `%I` for 12-hour clock.'

>>> assert '%'+'p' in content, \
'Value `%p` was not used; use `%p` for AM/PM.'

>>> assert type(result) is str, \
'Variable `result` has an invalid type; expected: `str`.'

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

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

# %% Imports
from datetime import datetime

# %% Types
result: str

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

# %% Result
result = ...