#### Iterating Through Submasks

C
f
```"""
Author : Syed Faizan (3rd Year Student IIIT Pune)
github : faizan2700
You are given a bitmask m and you want to efficiently iterate through all of
its submasks. The mask s is submask of m if only bits that were included in
bitmask are set
"""
from __future__ import annotations

def list_of_submasks(mask: int) -> list[int]:

"""
Args:
mask : number which shows mask ( always integer > 0, zero does not have any
submasks )

Returns:
all_submasks : the list of submasks of mask (mask s is called submask of mask
m if only bits that were included in original mask are set

Raises:
AssertionError: mask not positive integer

>>> list_of_submasks(15)
[15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
>>> list_of_submasks(13)
[13, 12, 9, 8, 5, 4, 1]
>>> list_of_submasks(-7)  # doctest: +ELLIPSIS
Traceback (most recent call last):
...
AssertionError: mask needs to be positive integer, your input -7
>>> list_of_submasks(0)  # doctest: +ELLIPSIS
Traceback (most recent call last):
...
AssertionError: mask needs to be positive integer, your input 0

"""

assert (
isinstance(mask, int) and mask > 0
), f"mask needs to be positive integer, your input {mask}"

"""
first submask iterated will be mask itself then operation will be performed
to get other submasks till we reach empty submask that is zero ( zero is not
included in final submasks list )
"""
all_submasks = []
submask = mask

while submask:
all_submasks.append(submask)
submask = (submask - 1) & mask

return all_submasks

if __name__ == "__main__":
import doctest

doctest.testmod()
```