Named integers and enums

[Peter Otten]

Hallvard B Furuseth wrote:

> Is this possible without too much code?
> 
>     class Named_int(object, int):
>         def __str__(self): return self.name
>         __repr__ = __str__
>         __slots__ = 'name'
>         # This does not work:
>         def __init__(self, name): self.name = name
>         # ...and it would be nice to freeze the name:
>         __setattr__ = __delattr__ = None
> 
>     x = Named_int(3, "foo")
>     print "%s = %d" % (x, x) # print "foo = 3"

You need __new__() instead of __init__():

<namedint.py>
class Int(int):
    _all = {}
    def __new__(cls, name, value):
        try:
            return cls._all[value]
        except KeyError:
            cls._all[value] = self = int.__new__(cls, value)
            self.name = name
            return self
    def __str__(self):
        return self.name
    def __repr__(self):
        return "%s:%s" % (self, int.__str__(self))
</namedint.py>

>>> from namedint import *
>>> debug, info, warn = map(Int, "DEBUG INFO WARN".split(), range(3))
>>> debug
DEBUG:0

Instances are cached in _all and thus only created once per value:

>>> Int("too late", 0)
DEBUG:0
>>> debug < info
1
>>> info + warn
3
>>>

Addition etc. will continue to return ints:

>>> info + warn
3

Peter