[Python-Dev] PEP 435 - ref impl disc 2 (original) (raw)

Ethan Furman ethan at stoneleaf.us
Tue May 14 04:36:56 CEST 2013

On 05/10/2013 10:15 PM, Glenn Linderman wrote:

So it is quite possible to marry the two, as Ethan helped me figure out using an earlier NamedInt class: class NIE( IntET, Enum ): x = ('NIE.x', 1) y = ('NIE.y', 2) z = ('NIE.z', 4) and then expressions involving members of NIE (and even associated integers) will be tracked... see demo1.py. But the last few lines of demo1 demonstrate that NIE doesn't like, somehow, remember that its values, deep down under the covers, are really int. And doesn't even like them when they are wrapped into IntET objects. This may or may not be a bug in the current Enum implementation.

[demo1.py excerpt] print( repr( NIE1( 1 ) + NIE1(2))) print( repr( NIE1( IntET('NIE1.x', 1 )) + NIE1(2)))

So the questions are: 1) Is there a bug in ref435 Enum that makes demo1 report errors instead of those lines working?

Nope.

2) Is something like demo2 interesting to anyone but me? Of course, I think it would be great for reporting flag values using names rather than a number representing combined bit fields.

No idea. ;)

3) I don't see a way to subclass the ref435 EnumMeta except by replacing the whole new method... does this mechanism warrant a slight refactoring of EnumMeta to make this mechanism easier to subclass with less code redundancy?

I've broken it down to make subclassing easier.

4) Or is it simple enough and useful enough to somehow make it a feature of EnumMeta, enabled by a keyword parameter?

Probably not.

5) All this is based on "IntET"... which likely suffices for API flags parameters... but when I got to truediv and rtruediv, which don't return int, then I started wondering how to write a vanilla ET class that inherits from "number" instead of "int" or "float"? One could, of course, make cooperating classes FloatET and DecimalET .... is this a language limitation, or is there more documentation I haven't read? :) (I did read footnote [1] of <http://docs.python.org/3/reference/datamodel.html#emulating-numeric-types>, and trembled.)

Sounds like a fun project (for some value of fun ;)

Okay, sorry for the long delay.

What it comes down to is if you want to marry two complex types together, you may have to be the counselor as well. ;)

Here's your code, revamped. I did make a slight change in the meta -- I moved the name assignment above the init call so it's available in init.

--8<-------------------------------------------------------- from ref435 import Enum from flags import IntET

class NIE1( IntET, Enum ): x = 1 y = 2 z = 4 def new(cls, value): member = IntET.new(cls, 'temp', value) member._value = value return member def init(self, value): self._etname = self._name

print( repr( NIE1.x.value )) print( repr( NIE1.x + NIE1.y )) print( repr( NIE1.x + ~ NIE1.y)) print( repr( NIE1.x + ~ 2 )) print( repr( NIE1.z * 3 ))

print( repr( NIE1( 1 ) + NIE1(2))) print( repr( NIE1( IntET('NIE1.x', 1 )) + NIE1(2))) --8<--------------------------------------------------------

and my results:

1 IntET('(x + y)', 3) IntET('(x + ~y)', -2) IntET('(x + -3)', -2) IntET('(z * 3)', 12) IntET('(x + y)', 3) IntET('(x + y)', 3)

Oh, and if you really wanted the 'NEI' in the _etname, change the name assignment:

 self._etname = 'NIE.' + self._name

-- Ethan

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