[Tutor] True and 1 [was Re: use of the newer dict types]

[Steven D'Aprano]

On 28/07/13 18:07, Alan Gauld wrote:
>> Comparison operators haven't depended on cmp() for a long time. You can
>> google "rich comparison operators" for more info:
>>
>> https://duckduckgo.com/?q=rich%20comparison%20operators
>
> I only read the first two but one question remains:
> If cmp() is gone is __cmp__() still supported? I'm assuming it
> must be for backward compatibility?

Not in Python 3, it's gone. In Python 3, you have to define all six the rich comparison methods __eq__ __ne__ __lt__ __gt__ __le__ __ge__ if you wish to support the comparison operators. There's a helper function in functools to help simplify the job:

@functools.total_ordering
class MyClass:
     ...


total_ordering will automatically fill in the missing comparison methods using rules like these:

"<=" is equivalent to "not >"
">=" is equivalent to "not <"
"!=" is equivalent to "not =="

"<=" is equivalent to "< or =="
">=" is equivalent to "> or =="



-- 
Steven