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Re: Enum questions.

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  Re: Enum questions. jmp <jeanmichel@sequans.com> - 2016-04-13 13:59 +0200

#106936 — Re: Enum questions.

On 04/13/2016 12:12 PM, Antoon Pardon wrote:
> I have been looking at the enum documentation and it
> seems enums are missing two features I rather find
> important.
>
> 1) Given an Enum value, someway to get the next/previous
>     one
>
> 2) Given two Enum values, iterate over the values between
>     them.
>
> Did I miss those in the documentation or are they really
> missing?
>

 From the doc :

"While Enum and IntEnum are expected to cover the majority of use-cases, 
they cannot cover them all. Here are recipes for some different types of 
enumerations that can be used directly, or as examples for creating 
one’s own."

I would disagree with you when you state that the features you mentioned 
are important. They could be useful, in certain cases but most of your 
code would better be agnostic to the enum value.

Now it is possible that you specifically work with a system where those 
features would be really useful. As mentioned by the documentation, 
subclassing Enum is possible:

tested with python 2.7

from enum import IntEnum

class UltimateEnum(IntEnum):
	@classmethod
	def range(cls, *args):
		enumToVal = lambda e: e.value if isinstance(e, cls) else e
		return (i for i in cls if i.value in range(*map(enumToVal, args)))

	@property
	def next(self):
		it = iter(self.__class__)
		try:
			for e in it:
				if e is self: return next(it)
		except StopIteration:
			return None
		return None

class Foo(UltimateEnum):
	A = 1
	B = 4
	C = 9
	D = 28


print "first to C:"
for f in Foo.range(Foo.C):
	print f

print "B to D :"
for f in Foo.range(Foo.B, Foo.D):
	print f

print "A to D+1 with step 2 : "
for f in Foo.range(Foo.A, Foo.D.value+1, 2):
	print f

print "next property"
print Foo.A.next
print Foo.C.next
print Foo.D.next

In [1]: run test.py
first to C:
Foo.A
Foo.B
B to D :
Foo.B
Foo.C
A to D+1 with step 2 :
Foo.A
Foo.C
next property
Foo.B
Foo.D
None


Hope it helps,

jm

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