Do we want to guarantee deepcopied attributes when converting ?

[cournape]

A reminiscence of #28:

# python >= 3.3, rough timing
import time

from attr import attributes, attr
from attr.validators import instance_of

def decode_if_needed(v):
    if isinstance(v, bytes):
        return v.decode()

@attributes
class Arch(object):
    name = attr("name")

@attributes
class ConvertedArch(object):
    name = attr("name", validator=instance_of(str), convert=decode_if_needed)

def timeit(func):
    times = []
    for i in range(10000):
        start = time.perf_counter()
        func()
        times.append(time.perf_counter() - start)
    return "Min cost across 10000 iterations: {:.2f} us".format(min(times) * 1e6)

print(timeit(lambda: Arch("x86")))
print(timeit(lambda: ConvertedArch(b"x86")))

Min cost across 10000 iterations: 1.40 us
Min cost across 10000 iterations: 43.72 us

Now, the fix may not be as trivial as #28, because I can see how it may be part of the API that the original attribute is not touched when using convert, and not using fields to iterate in https://github.com/hynek/attrs/blob/master/src/attr/_make.py#L447 would break that promise. As I have not seen any test related to this, maybe that promise could be relaxed ?

[hynek]

Eh could you rephrase + elaborate please? I have a nasty head cold and can’t entirely follow. :)

[cournape]

Let me try again :)

As in #28, the speed difference is because we iterate over the attr descriptors using fields, which makes a deepcopy for every field.

In #28, we've fixed it by iterating using inst.__class__.__attrs_attrs__. I was about to prepare a PR to do the same here, but then realized that the deepcopy may have bene intentional in this case. If not, I will be happy to prepare a PR to fix this.

[hynek]

Um this would only matter, if someone would modify the attribute list in their container, right? (which they never should)

[cournape]

Ok, let me prepare a PR then.

What is the rationale for using deepcopy in fields then ?

[hynek]

I find there’s a difference between a public API like fields and misbehaving in an converter. But maybe I’m wrong. :)

[hynek]

do you think you can get it done by say Wed? I’d like to push out a release before PyCon

[cournape]

looks like I could ! Too bad I could not make it up this year at PyCon...

[hynek]

aw :(