Bitmask testing routine for Python 3.6+

test_bitmask.py

# Copyright (C) 2019 Chris Lawrence
# You may freely modify, copy, and reuse this software under the terms of the MIT License.

def test_bitmask(value: int, mask: str) -> bool:
    mask = mask.replace("_", "")
    testval: int = 1
    for bit in reversed(mask):
        if bit == '1' and not (value & testval):
            return False
        elif bit == '0' and (value & testval):
            return False
        elif bit != "x":
            raise ValueError('Invalid bitmask character: '+bit)
        testval <<= 1
    return True

assert( test_bitmask(0x80, '1xxx_xxxx') == True )
assert( test_bitmask(0x3f, '0xx1_xxxx') == True )
assert( test_bitmask(0x3f, '0xx1_xxx0') == False )
assert( test_bitmask(0xff, '0xx1_xxx0') == True ) # Should fail