[Python-ideas] IntFlags

[Andrew Barnert]

On Mar 4, 2015, at 7:44, Neil Girdhar <mistersheik at gmail.com> wrote:

> Why do you need these composite flags?

Because the whole point of this proposal is to deal with C types (otherwise, who cares about the int value?). And most such C types define combined values--the motivating example, stat, has S_IRWXU, etc. If the Python code is less readable than the equivalent C code...

> On Wed, Mar 4, 2015 at 10:31 AM, Chris Angelico <rosuav at gmail.com> wrote:
>> On Thu, Mar 5, 2015 at 2:17 AM, Andrew Barnert
>> <abarnert at yahoo.com.dmarc.invalid> wrote:
>> > Another issue that came up was that C flags often have "combined" names that are ambiguous: RDWR = RDONLY | WRONLY), which is fine until you want a repr (in C, it's just going to print 3); does it have to be smart enough to show RDWR? (Or, worse, RDWR | CLOEXEC.)
>> >
>> 
>> That could probably be handled by going through the flags in iteration
>> order. If the flag is present, emit it and move on. Something like
>> this:
>> 
>> from enum import IntEnum
>> 
>> class Flags(IntEnum):
>>     RDWR = 3
>>     RDONLY = 1
>>     WRONLY = 2
>>     CLOEXEC = 4
>> 
>> def flag_str(flg):
>>     names = []
>>     for flag in Flags:
>>         if (flg&flag) == flag:
>>             flg -= flag
>>             names.append(str(flag))
>>     return "|".join(names)
>> 
>> print(flag_str(Flags.RDWR|Flags.CLOEXEC))
>> print(flag_str(Flags.RDONLY|Flags.CLOEXEC))
>> 
>> 
>> As long as the combined versions come up ahead of the others, they'll
>> be used. Alternatively, if you prefer them _not_ to be used, just put
>> them after the individual forms, and then the str() will expand them
>> out.
>> 
>> ChrisA
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