On 5/28/2021 12:08 AM, Michał Górny wrote:
On Thu, 2021-05-27 at 20:24 -0700, Ethan Furman wrote:
Greetings!
The Flag type in the enum module has had some improvements, but I find it
necessary to move one of those improvements
into a decorator instead, and I'm having a hard time thinking up a name.
What is the behavior? Well, a name in a flag type can be either canonical (it
represents one thing), or aliased (it
represents two or more things). To use Color as an example:
class Color(Flag):
RED = 1 # 0001
GREEN = 2 # 0010
BLUE = 4 # 0100
PURPLE = RED | BLUE # 0101
WHITE = RED | GREEN | BLUE # 0111
The flags RED, GREEN, and BLUE are all canonical, while PURPLE and WHITE are
aliases for certain flag combinations. But
what if we have something like:
class Color(Flag):
RED = 1 # 0001
BLUE = 4 # 0100
WHITE = 7 # 0111
As you see, WHITE is an "alias" for a value that does not exist in the Flag
(0010, or 2). That seems like it's probably
an error. But what about this?
class FlagWithMasks(IntFlag):
DEFAULT = 0x0
FIRST_MASK = 0xF
FIRST_ROUND = 0x0
FIRST_CEIL = 0x1
FIRST_TRUNC = 0x2
SECOND_MASK = 0xF0
SECOND_RECALC = 0x00
SECOND_NO_RECALC = 0x10
THIRD_MASK = 0xF00
THIRD_DISCARD = 0x000
THIRD_KEEP = 0x100
Here we have three flags (FIRST_MASK, SECOND_MASK, THIRD_MASK) that are
aliasing values that don't exist, but it seems
intentional and not an error.
So, like the enum.unique decorator that can be used when duplicate names should
be an error, I'm adding a new decorator
to verify that a Flag has no missing aliased values that can be used when the
programmer thinks it's appropriate... but
I have no idea what to call it.
Any nominations?
Maybe something like the following would be a good starting point:
@bitmask_require_individual_bits
@all_bits_defined
or
@unique_bits
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