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Attrs – the Python library everyone needs (2016)

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Re: Attrs – the Python library everyone needs (2016)

#41

Post by ledauphin »

bjourne wrote: post #22

Costs: Depending on a relatively unknown library. Using arcane class decorators and unusual syntactic constructs: @attr.s and x = attr.ib() (a pun?). Benefits: Saving at best 10-15 lines of boilerplate per data class. Much less if namedtuple works for you. If you want to save lines in __init__ you can write "for k, v in locals().items(): setattr(self, k, v)". But you shouldn't. Edit: Forgot to add to the most importa…

there are newer (since 2020) syntactic constructs that might be more to your liking. take a look at the docs again.

Incidentally, I'd recommend against Named Tuples for non-trivial software. Because they can be indexed by integer and unpacked like tuples, additions of new fields are backwards-incompatible with existing code.

Re: Attrs – the Python library everyone needs (2016)

#42

Post by nauticacom »

I've never understood the appeal of these "define struct-like-object" libraries (in any language; I've never understood using the standard library's "Struct" in Ruby). My preferred solution for addressing complexity is also to decompose the codebase into small, understandable, single-purpose objects, but so few of them end up being simple value objects like Point3D. Total ordering and value equality make sense for value objects but not much else, so it really doesn't improve understandability or maintenance that much. And concerns like validation I would never want to put in a library for object construction. In web forms where there are a limited subset of rules I always want to treat the same way, sure, but objects have much more complicated relationships with their dependencies that I don't see much value in validating them with libraries.

Overall, I really don't see the appeal. It makes the already simple cases simpler (was that Point3D implementation really that bad?) and does nothing for the more complicated cases which make up the majority of object relationships.

Re: Attrs – the Python library everyone needs (2016)

#43

Post by ledauphin »

flohofwoe wrote: post #16

...or one could just use Python without classes, just functions. TBH I never quite understood why Python has the class keyword, it's a much better language without.

attrs really isnt about OO-style classes - it's specifically meant to provide struct-like declarative data containers, and these can help bridge the gap between the toolset that Python provides and functional (data-first) programming styles.

Re: Attrs – the Python library everyone needs (2016)

#45

Post by [deleted] »

nauticacom wrote: post #42

I've never understood the appeal of these "define struct-like-object" libraries (in any language; I've never understood using the standard library's "Struct" in Ruby). My preferred solution for addressing complexity is also to decompose the codebase into small, understandable, single-purpose objects, but so few of them end up being simple value objects like Point3D. Total ordering and value equality make sense for va…

[deleted]

Re: Attrs – the Python library everyone needs (2016)

#46

Post by atorodius »

nauticacom wrote: post #42

I've never understood the appeal of these "define struct-like-object" libraries (in any language; I've never understood using the standard library's "Struct" in Ruby). My preferred solution for addressing complexity is also to decompose the codebase into small, understandable, single-purpose objects, but so few of them end up being simple value objects like Point3D. Total ordering and value equality make sense for va…

well one appeal is that you dont have to write constructors, that‘s already enough of a win for me. then you get sane eq, and sane str, and already you remove 90% boilerplate

Re: Attrs – the Python library everyone needs (2016)

#47

Post by joshuamorton »

nauticacom wrote: post #42

I've never understood the appeal of these "define struct-like-object" libraries (in any language; I've never understood using the standard library's "Struct" in Ruby). My preferred solution for addressing complexity is also to decompose the codebase into small, understandable, single-purpose objects, but so few of them end up being simple value objects like Point3D. Total ordering and value equality make sense for va…

Ignore all of the validation aspects. In python, you have tuples, (x, y, z), then you have namedtuples and then attrs/dataclasses/pydantic-style shorthand classes.

These are useful even if only due to the "I can take the three related pieces of information I have and stick them next to each other". That is, if I have some object I'm modelling and it has more than a single attribute (a user with a name and age, or an event with a timestamp and message and optional error code), I have a nice way to model them.

Then, the important thing is that these are still classes, so you can start with

    @dataclass
    class User:
        name: str
        age: int
and have that evolve over time to

    @dataclass
    class User:
        name: str
        age: int
        ...
        permissions: PermissionSet
        
        @property
        def location():
            # send off an rpc, or query the database for some complex thing.
and since it's still just a class, it'll still work. It absolutely makes modelling the more complex cases easier too.

Re: Attrs – the Python library everyone needs (2016)

#48

Post by atorodius »

ledauphin wrote: post #41
bjourne wrote: post #22

Costs: Depending on a relatively unknown library. Using arcane class decorators and unusual syntactic constructs: @attr.s and x = attr.ib() (a pun?). Benefits: Saving at best 10-15 lines of boilerplate per data class. Much less if namedtuple works for you. If you want to save lines in __init__ you can write "for k, v in locals().items(): setattr(self, k, v)". But you shouldn't. Edit: Forgot to add to the most importa…

there are newer (since 2020) syntactic constructs that might be more to your liking. take a look at the docs again. Incidentally, I'd recommend against Named Tuples for non-trivial software. Because they can be indexed by integer and unpacked like tuples, additions of new fields are backwards-incompatible with existing code.

yeah this has bitten me before. combine it with overwriting len for a namedtuple and you have a proper mess

Re: Attrs – the Python library everyone needs (2016)

#49

Post by atorodius »

This is only remotely relevant but I recently learned that the related `dataclasses` is implemented by constructing _string representations_ of functions and calling `exec` on them.

https://github.com/python/cpython/blob/3.10/Lib/dataclasses....

Kind of blew my mind

Re: Attrs – the Python library everyone needs (2016)

#50

Post by rthomas6 »

flohofwoe wrote: post #16

...or one could just use Python without classes, just functions. TBH I never quite understood why Python has the class keyword, it's a much better language without.

I thought like you for several years. Then one day, I needed a custom type. You can use dicts (or lists, or namedtuples, I guess?), but it just ends up being cleaner and more idiomatic to define a class for the type, because you can define common methods for them.

The article mentions quaternions. If you make a quaternion type (class), you can define addition, multiplication, comparison, etc. for it (methods). If you represent a quaternion any other way, you can't say a * b. Or maybe you can, but I don't know how.

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