PEP Idea: Multi-get for lists/tuples and dictionaries (inspired in NumPy)

[Pieter van Oostrum]

Santiago Basulto <santiago.basulto at gmail.com> writes:

> Hello community. I have an idea to share with the list to see what you all
> think about it.
>
> I happen to use both Python for Data Science (with our regular friends
> NumPy and Pandas) as well as for scripting and backend development. Every
> time I'm working in server-side Python (not the PyData stack), I find
> myself missing A LOT features from NumPy, like fancy indexing or boolean
> arrays.
>
> So, has it ever been considered to bake into Python's builtin list and
> dictionary types functionality inspired by NumPy? I think multi indexing
> alone would be huge addition. A few examples:
>
> For lists and tuples:
>     >>> l = ['a', 'b', 'c']
>     >>> l[[0, -1]]
>     ['a', 'c']
>
> For dictionaries it'd even be more useful:
>     d = {
>         'first_name': 'Frances',
>         'last_name': 'Allen',
>         'email': 'fallen at ibm.com'
>     }
>     fname, lname = d[['first_name', 'last_name']]
>
> I really like the syntax of boolean arrays too, but considering we have
> list comprehensions, seems a little more difficult to sell.
>
> I'd love to see if this is something people would support, and see if
> there's room to submit a PEP.

How about implementing it yourself:

In [35]: class MultiDict(dict):
     ...     def __getitem__(self, idx):
     ...         if isinstance(idx, list):
     ...             return [self[i] for i in idx]
     ...         return super().__getitem__(idx)

In [36]: d = MultiDict({
     ...         'first_name': 'Frances',
     ...         'last_name': 'Allen',
     ...         'email': 'fallen at ibm.com'
     ...     })

In [37]: d
Out[37]: {'first_name': 'Frances', 'last_name': 'Allen', 'email': 'fallen at ibm.com'}

In [38]: d['email']
Out[38]: 'fallen at ibm.com'

In [39]: d[['first_name', 'last_name']]
Out[39]: ['Frances', 'Allen']

The implementation of other methods, like __setitem__ and __init__, and maybe some more subtle details like exceptions, is left as an exercise for the reader.
-- 
Pieter van Oostrum
www: http://pieter.vanoostrum.org/
PGP key: [8DAE142BE17999C4]