Python

a use case -- feature flags

Mix and match to plan your day

will i be going home today?

>>> OUTRAGED_BY_NEWS = 0b00000001
>>> GET_A_COFFEE = 0b00000010
>>> GO_FOR_A_HIKE = 0b00000100
>>> GO_FOR_A_RUN = 0b00001000
>>> GO_HOME = 0b00010000 
>>> various_flags_ored_together = GET_A_COFFEE | GO_FOR_A_RUN | GO_HOME
>>> various_flags_ored_together & GO_HOME == GO_HOME
True
>>> various_flags_ored_together & GO_FOR_A_HIKE == GO_FOR_A_HIKE
False
>>> various_flags_ored_together = GET_A_COFFEE | GO_FOR_A_RUN | GO_HOME
>>> bin(various_flags_ored_together)
'0b11010'
>>> various_flags_ored_together & OUTRAGED_BY_NEWS == OUTRAGED_BY_NEWS
>>> False
>>> bin(OUTRAGED_BY_NEWS)
>>> '0b1'
>>> various_flags_ored_together >> OUTRAGED_BY_NEWS
>>> bin(various_flags_ored_together)
'0b1101'

Guess haven't gone for a hike today...maybe tomorrow

right shift removes bit at flag position. Which, in this case, happens to correspond to the right most bit.

use case -- file access permissions

For those looking to check file access permissions there is the stat module

>>> import stat
>>> from pathlib import Path
>>> path_f = Path.home().joinpath(".bashrc")
>>> stat.S_IRUSR
256
>>> path_f.stat().st_mode
33188
>>> is_owner_read = path_f.stat().st_mode & stat.S_IRUSR == stat.S_IRUSR
>>> is_owner_read
True
>>> path_f = Path("/etc/fstab")
>>> is_other_write = path_f.stat().st_mode & stat.S_IWOTH == stat.S_IWOTH
>>> is_other_write
False

Assumes ~/.bashrc exists, if not choose a different file you are owner and have read access to.

path_f.stat().st_mode & stat.S_IRUSR == stat.S_IRUSR

Looking thru the mundane file (not Linux access control list) permissions. All those flags are crammed into st_mode. In st_mode, on/off bit at 2^8 is that on?

Sources

read user access stat.S_IRUSR

write others access stat.S_IWOTH

os.stat_result

pathlib.Path.stat