[Python-ideas] Consider adding an iterable option to dataclass

[Eric V. Smith]

On 8/10/2018 7:01 PM, Neil Girdhar wrote:
> It would be nice if dataclasses 
> (https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass) 
> had an option to make them a sequence.  This would make
> 
> dataclass(frozen=True, order=True, sequence=True)
> 
> an optionally-typed version of namedtuple.  It would almost totally 
> supplant it except that namedtuples have a smaller memory footprint.

Note that type.NamedTuple already gives you typed namedtuples. 
Admittedly the feature set is different from dataclasses, though.

> sequence would simply inherit from collections.abc.Sequence and 
> implement the two methods __len__ and __getitme__.

Unless I'm misunderstanding you, this falls in to the same problem as 
setting __slots__: you need to return a new class, in this case since 
you can't add inheritance after the fact. I don't think 
__isinstancecheck__ helps you here, but maybe I'm missing something (I'm 
not a big user of inheritance or ABCs).

Not that returning a new class is impossible, it's just that I didn't 
want to do it in the first go-round with dataclasses.

For slots, I have a sample @add_slots() at 
https://github.com/ericvsmith/dataclasses/blob/master/dataclass_tools.py. 
Maybe we could do something similar with @add_sequence() and test it 
out? It would have to be a little more sophisticated than @add_slots(), 
since it would need to iterate over __dataclass_fields__, etc.

I'm on vacation next week, maybe I'll play around with this.

Eric