MultiEnum

An enumeration type supporting multiple equivalent names.

Rationale

I find the types defined in the built-in enum type in Python 3 to be clumsy and hard to use for my purposes. Further, I have a project which repeatedly requires me to resolve strings to numbers and then back to sometimes different strings, based on the context. This module is the result of that.

The implementation subclasses int, which allows for the value of the enumeration to be stored in a minimal amount of space, while providing a number of attributes of the object for converting it to different names.

Usage

Subclasses should define the class attribute _members as a tuple of tuples. [1] Every member of _members should be a tuple of strings containing a name which equates to the enumerated value. The value will be inferred from the member's position in the tuple (equal to the subscript). Optionally, a subclass may define _fields, a tuple of field names which correspond to the order the enumeration names appear in within the _members attribute.

The enumerated value can be instantiated with a plain int value or with any of the names provided in _members, either using the appropriate field name as a keyword or, so long as it is unique across all fields, as an un-keyworded argument. There is no test to ensure that names are unique -- if a name appears multiple times in the _members tuples, the behavior is undefined.

By default, the first in each individual enumerated tuple will be returned if the value is cast as a string (using the str() function, for instance). For compatability with the types in the enum module, the same value will be returned using the name attribute. The other names are available as a tuple in the _names attribute, and if _fields was defined, will be available as the value of attributes corresponding to the relevant field name in _fields.

If more than one argument is given on instantiation, either keyworded or not, a ValueError exception will be raised unless all arguments resolve to the same value.

The MultiEnum type makes an attempt to be idempotent -- i.e., if x is an MultiEnum, x is MultiEnum(x) should be true. However, in the case of multiple init values, idempotency is only preserved for the first positional parameter. x is MultiEnum(a, x) will not be true, even if a and x are equal.

[1]	Techincally, the _members attribute, all members of _members, and the _fields attribute can be any iterable sequence. I strongly recommend tuples unless you have a reason not to, because in addition to being lightweight and simple, they're immutable, which saves the interpreter a lot of work.

Example

>>> from multienum import MultiEnum
>>> class SampleEnum(MultiEnum):
...   _members = (("zero", "zip", "zéro", "cero"),
...               ("one", "ace", "une", "uno"),
...               ("two", "deuce", "deux", "dos"))
...   _fields = ('english', 'slang', 'french', 'spanish')
>>> val1 = SampleEnum("one")
>>> int(val1)
1
>>> str(val1)
'one'
>>> val1.name
'one'
>>> val1.spanish
'uno'
>>> val2 = SampleEnum(slang="deuce")
>>> int(val2)
2
>>> try:
...   se = SampleEnum("two", spanish="cero")
... except ValueError:
...   print("Value mismatch")
Value mismatch