[Python-Dev] PEP 557: Data Classes

Ethan Furman ethan at stoneleaf.us
Mon Sep 18 14:37:09 EDT 2017

On 09/11/2017 03:28 PM, Guido van Rossum wrote:

> Oddly I don't like the enum (flag names get too long that way), but I do agree with everything else Barry said (it
> should be a trivalue flag and please don't name it cmp).

Hmmm, named constants are one of the motivating factors for having an Enum type.  It's easy to keep the name a 
reasonable length, however: export them into the module-level namespace.  re is an excellent example; the existing flags 
were moved into a FlagEnum, and then (for backwards compatibility) aliased back to the module level:

     class RegexFlag(enum.IntFlag):
         ASCII = sre_compile.SRE_FLAG_ASCII # assume ascii "locale"
         IGNORECASE = sre_compile.SRE_FLAG_IGNORECASE # ignore case
         LOCALE = sre_compile.SRE_FLAG_LOCALE # assume current 8-bit locale
         UNICODE = sre_compile.SRE_FLAG_UNICODE # assume unicode "locale"
         MULTILINE = sre_compile.SRE_FLAG_MULTILINE # make anchors look for newline
         DOTALL = sre_compile.SRE_FLAG_DOTALL # make dot match newline
         VERBOSE = sre_compile.SRE_FLAG_VERBOSE # ignore whitespace and comments
         A = ASCII
         I = IGNORECASE
         L = LOCALE
         U = UNICODE
         M = MULTILINE
         S = DOTALL
         X = VERBOSE
         # sre extensions (experimental, don't rely on these)
         TEMPLATE = sre_compile.SRE_FLAG_TEMPLATE # disable backtracking
         T = TEMPLATE
         DEBUG = sre_compile.SRE_FLAG_DEBUG # dump pattern after compilation

So we can still do re.I instead of re.RegexFlag.I.

Likewise, if we had:

     class Compare(enum.Enum):
         NONE = 'each instance is an island'
         EQUAL = 'instances can be equal to each other'
         ORDERED = 'instances can be ordered and/or equal'

then we can still use, for example, EQUAL, but get the more informative repr and str when we need to.


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