[Python-Dev] Overloading comparison operator for lists

Cameron Simpson cs at cskk.id.au
Mon May 27 00:12:12 EDT 2019

This belongs on python-ideas, not python-dev. I've directed replies to 
this message there. Comments below.

On 26May2019 21:52, Montana Burr <montana.burr at gmail.com> wrote:
>NumPy arrays have this awesome feature, where array == 3 does an
>element-wise comparison and returns a list. For example:
>It would be cool if Python had similar functionality for lists.

map(lamdba item: item==3, [1,2,3,4,5])

I'm not sure this rates extra Python features.

Personally I'm -1 on this suggestion because == traditionally returns a 
Boolean, NumPy notwithstanding. Your example above doesn't return a 

>If that is not possible, perhaps we could consider allowing developers 
>to overload operators on built-in types within the context of a project or
>module. For example, an overload in one module would have no effect on the
>same operator in a different module (such as any Python standard modules.)

This is usally done by overloading dunder methods on classes. if you 
class subclasses a builtin eg int or list then the instances get the 
special behaviour.

>Additionally, let's then give the developers the option to explicitly
>import an overload from other modules. So, people could develop a module
>with the  purpose of providing overloads that make complete sense within a
>certain context.

If you go the subclass route you could do this with a mixin class (a 
class providing methods but little else, intended to be part of the MRO 
of a subclass).

Cameron Simpson <cs at cskk.id.au>

More information about the Python-Dev mailing list