[Python-ideas] str-type enumerations

[Ethan Furman]

On 04/04/2013 09:06 AM, Eli Bendersky wrote:
>
> On Thu, Apr 4, 2013 at 8:11 AM, Ethan Furman wrote:
>
>     On 04/04/2013 06:56 AM, Eli Bendersky wrote:
>
>         On Wed, Apr 3, 2013 at 8:23 PM, Eli Bendersky wrote:
>
>             On Tue, Apr 2, 2013 at 12:25 PM, Ethan Furman wrote:
>
>                 I'm not trying to beat this dead horse (really!) but back when the enumeration discussions were going
>                 fast and
>                 furious one of the things asked for was enumerations of type str, to which others replied that strings named
>                 themselves.
>
>                 Well, I now have a good case where I don't want to use the string that names itself: 'Mn$(1,6)'  I would
>                 match
>                 rather write item_code!  :)
>
>
>             The latest incarnation of flufl.enum that went through the round of discussions during PyCon allows string
>             values in
>             enumerations, if you want them:
>
>             >>> from flufl.enum import Enum
>             >>> class WeirdNames(Enum):
>             ...   item_code = 'Mn$(1,6)'
>             ...   other_code = '#$%#$^'
>             ...
>             >>> WeirdNames.item_code
>             <EnumValue: WeirdNames.item_code [value=Mn$(1,6)]>
>             >>> i = WeirdNames.item_code
>             >>> i
>             <EnumValue: WeirdNames.item_code [value=Mn$(1,6)]>
>             >>> i.value
>             'Mn$(1,6)'
>             >>> print(i)
>             WeirdNames.item_code
>
>             I haven't updated PEP 435 to reflect this yet, hope to do so in the next day or two.
>
>
>         The PEP is up-to-date now, and mentions string-valued enums as well.
>
>
>     Wow -- looks like flufl.enum has come a long way!  Cool.
>
>     My use case for the str enum is to use it as a dict key for a custom mapping to a Business Basic file; this means
>     that the str value will be pulled apart and disected to see exactly where in a fixed-length field it needs to pull
>     data from (in the example above it would be the first six characters as BB is 1-based).
>
>     Will a str-based enum handle that, or will the custom mapping have to be updated to check for a str or an enum, and
>     if an enum use the .value?
>
>
> I'm not entirely sure what you mean here, Ethan. What I do know is that enumeration values are hashable, so they can be
> used as keys in dictionaries.

In the example above 'Mn$' is the field, and '(1,6)' are the first six charecters in the field.  So the custom mapping 
has to parse the key passed to in in order to return the proper value; it looks something like this:

     def __getitem__(self, key):
         real_key = key[:3]
         field = self.dict[real_key]
         first, length = key[3:][1:-1].split(',')
         first = first - 1
         last = first + length
         data = field[first:last]
         return data

If key is a str-based enum, will this work?

--
~Ethan~