On Fri, Apr 28, 2017 at 4:55 AM, Tin Tvrtković <tinches...@gmail.com> wrote:
> I'm going to posit we need declarative classes. (This is what a library
> like attrs provides, basically.) For a class to be declarative, it needs to
> be possible to inspect the class for its attributes and more.
>
> I'm putting forward three examples. These examples are based on attrs
> since that's what I consider to be the best way of having declarative
> classes in Python today.
>
My favorite example of declarative classes in Python today is Python
3.6.1's typing.NamedTuple:
class Employee(NamedTuple):
"""Represents an employee."""
name: str
id: int = 3
NamedTuple fixes many of the warts of the original namedtuple:
1. It supports docstrings out of the box, not requiring a subclass (which
require setting __slots__ to get right)
2. It supports default values.
3. It has a sane declarative syntax.
4. It's fields can be type checked.
What's not to love? There are two valid complaints [1] about namedtuple
that still apply:
1. It's a tuple, which brings along extra baggage (numeric
indexing/iteration, comparing equal to tuples, etc.)
2. It's immutable. Sometimes it's convenient to have a mutable class.
It seems like a simple solution would be make variants of NamedTuple that
solve each of these issues. We might call these collections.Struct and
collections.FrozenStruct.
[1] e.g., see https://glyph.twistedmatrix.com/2016/08/attrs.html
> Third example: I work at a mobile games company. The backends are Python,
> the games are written in other languages. The backends and the games share
> data structures - requests, responses, the save game, game data. I want to
> have a single source of truth for these structures, so I want to generate
> classes/structs in other languages from the backend Python classes.
>
If you're willing to define these classes outside of Python in a separate
file (which is quite reasonable if you need cross-language support), then
this is exactly the problem solved by protocol buffers (
https://developers.google.com/protocol-buffers/). So I'm not sure we really
need this fix in Python.
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