[issue29594] implementation of __or__ in enum.auto

[Ethan Furman]

Ethan Furman added the comment:

Serhiy, agreed.  Closing.

Marc, thanks, I see I missed supporting non-auto() combinations.  Feel free to 
open an issue for that at:

  https://bitbucket.org/stoneleaf/aenum

Either way I'll get that fixed.

--
resolution:  -> rejected
stage:  -> resolved
status: open -> closed

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[issue29594] implementation of __or__ in enum.auto

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

I don't think it is worthwhile. Using underscored names looks pretty pythonic 
to me.

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[issue29594] implementation of __or__ in enum.auto

[Marc Guetg]

Marc Guetg added the comment:

@ethan, didn't know about aenum, thanks for showing it to me. However it 
doesn't seem to support the behavior I'm after (or I'm doing something wrong)

import aenum

try:
class Foo(aenum.Flag):
a = aenum.auto()
b = a | aenum.auto()
except Exception as err:
print(err)

try:
class Bar(aenum.Flag):
a = aenum.auto()
b = aenum.auto() | a
except Exception as err:
print(err)

results in 
unsupported operand type(s) for |: 'int' and 'auto'
exceptions must derive from BaseException

where the latter might be a bug in the implementation.


I do realize that I'm stuck with this for the moment. My motivation with 
opening this thread was that I was wondering if such a feature would be 
worthwhile for the community. In case there is interest in this feature I would 
try to run the unit test and follow all the steps to try to push it through. 
However I save myself the work in case the community decides that the 
implementation is not worth it. Which would also be fine with me, as I monkey 
patched it for my code - so no problem on my end.

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[issue29594] implementation of __or__ in enum.auto

[Ethan Furman]

Ethan Furman added the comment:

aenum 2.0 [1] has been released.  Because it also covers Python 2.7 I had to 
enhance its auto() to cover |, &, ^, and ~ so that Enum classes could be 
properly created.

At this moment your choices are to use odd naming or aenum (with its enhanced 
auto).


[1] https://pypi.python.org/pypi/aenum

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assignee:  -> ethan.furman

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[issue29594] implementation of __or__ in enum.auto

[Ethan Furman]

Ethan Furman added the comment:

I also think using leading underscores is a better way to signal that a 
particular value is "weird".

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[issue29594] implementation of __or__ in enum.auto

[Ethan Furman]

Ethan Furman added the comment:

@Julian: Giving flag combinations their own name can be useful.  For example, 
instead of seeing Color.GREEN|RED one can see Color.YELLOW .

@Marc: I'm not convinced this is a needed change as it doesn't seem to be a 
common method, nor one that cannot be easily implemented independently (perhaps 
as a recipe in the docs).

Are you aware of other enumerations that take this approach?

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[issue29594] implementation of __or__ in enum.auto

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

Just make C and D protected or private.

class Foo(Flag):
A = auto()
B = auto()
AB = A | B
_C = auto()
__D = auto()
AC = A | _C
ABD = A | B | __D

--
nosy: +serhiy.storchaka

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[issue29594] implementation of __or__ in enum.auto

[Marc Guetg]

Marc Guetg added the comment:

One made-up use-case would be:

class LogLevel(Flags):
start = auto()
log1 = start | auto()
log2 = start | auto()


def fun(flags, *args):
if start in flags:
# open log file

if log1 in flags:
   # Log important thing 1

if log2 in flags:
   # Log important thing 2

if start in flags:
   # close log file


Alternatively the same could be achieved using the existing capabilities with:

class LogLevel(Flags):
 start = auto()
 _log1 = auto()
 log1 = start | _log1
 _log2 = auto()
 log2 = start | _log2

Which is less clear imho and could potentially a problem if somebody uses 
LogLevel._log2


Another alternative would be that within the function we would check for all 
cases. eg:

if (start in flags) or (log1 in flags) or (log2 in flags):

Which leads to less clear code and makes the code less maintainable when log3 
gets introduced. In the existing case we need to remember to change the if 
clause both when opening and closing the file. After the proposed change we 
only need to change the enum.

I'm sure there are more use-cases for it. The one I'm using it for is a bit 
more convoluted that's why I'm not presenting it here.

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[issue29594] implementation of __or__ in enum.auto

[Julien Palard]

Julien Palard added the comment:

Your implementation looks right, but I don't see the point of defining 
combinations AB, AC, ABD in the Foo enum. Foo may only define A, B, C, D and 
outside of Foo anyone can build any needed combinations.

This way it looks clear in the Foo declaration (4 lines, 4 auto()). Did I 
missed a usefull usage of declaring combination inside the enum?

--
nosy: +mdk

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[issue29594] implementation of __or__ in enum.auto

[Berker Peksag]

Changes by Berker Peksag :


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nosy: +ethan.furman

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[issue29594] implementation of __or__ in enum.auto

[Marc Guetg]

Changes by Marc Guetg :


--
title: implement __or__ in enum.auto -> implementation of __or__ in enum.auto

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