container.___le___ can use only <=?

[Carl Banks]

On Dec 14, 4:15 pm, Neil Cerutti <horp... at yahoo.com> wrote:
> When implementing the rich comparison operators for some sort of
> container, it's tempting to save code by doing something like:
>
>  class LarchTree:
>    ...
>    def __gt__(self, other):
>      # A lot of code to traverse the tree
>    def __le__(self):
>      return not self > other
>
> However, if I'm thinking correctly, this is a bad idea. The
> reasoning being that > and <= are not required to be each others
> opposite for arbitrary value types, and may not even both be
> supplied by the contained objects.

And yet, by the same reasoning, using > and <= for list and tuple is
also a "bad idea".


> If a LarchTree user stores objects that don't support __gt__,
> will he have a legitimate complaint when using LarchTree.__le__
> results in an attribute error?

No.


Carl Banks