[Python-ideas] "Exposing" `__min__` and `__max__`

[Pål Grønås Drange]

Well, numpy implements ndarray.min(). It would be very nice if
min(np.array) worked as expected.

Pål

On 19 Jun 2018 21:33, "Michael Selik" <mike at selik.org> wrote:

> Do you mind sharing an example usage in a realistic context? There might
> be a good solution that doesn't require adding magic methods.
>
>
> On Tue, Jun 19, 2018, 12:24 PM James Edwards <jheiv at jheiv.com> wrote:
>
>> I've only recently looked for these special methods, so that in and of
>> itself may be the reason these methods aren't exposed, but I could think of
>> objects that may wish to implement __min__ and __max__ themselves, for
>> efficiency.  For example:
>>
>>     # A "self-sorted" list object
>>     class AlwaysSortedListObejct:
>>         def __min__(self): return self.lst[0]
>>         def __max__(self): return self.lst[-1]
>>
>>
>>     # An object that maintains indices of extrema (e.g. for complex
>> comparisons)
>>     class KeepsTrackOfExtrema:
>>         def __init__(self):
>>             self.min_index = None
>>             self.max_index = None
>>
>>         def append(self, obj):
>>             new_index = len(obj)
>>             self.backer.append(obj)
>>
>>             if (self.max_index is None) or (obj >
>> self.backer[self.max_index]):
>>                 self.max_index = new_index
>>
>>             if (self.min_index is None) or (obj <
>> self.backer[self.min_index]):
>>                 self.min_index = new_index
>>
>>         def __min__(self): return self.backer[self.min_index]
>>         def __max__(self): return self.backer[self.max_index]
>>
>> Where these methods be called via the single-argument calls to `max(obj)`
>> and `min(obj)`.
>>
>> If it's not clear, it'd be similar to the way __len__ is called (when
>> defined) via len(obj).
>>
>> My solution was to implement a .min() method, but that caused some ugly
>> special casing when the object could also be a regular list (where I'd want
>> to iterate over all of the items).
>>
>> I searched the list, but has this been discussed before?  Is there any
>> merit in it?
>>
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>
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