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From: Hynek Schlawack <hs@ox.cx>
Newsgroups: comp.lang.python.announce
Subject: attrs 16.3.0
Date: Sat, 26 Nov 2016 14:57:13 +0100
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Xref: csiph.com comp.lang.python.announce:2326

Dear fellow Pythonistas,

I=E2=80=99m very happy to announce attrs 16.3.0, the Python library the =
makes you love writing classes again!  If you need a refresher why you =
should use attrs, have a look at =E2=80=9CThe One Python Library =
Everyone Needs=E2=80=9D =
<https://glyph.twistedmatrix.com/2016/08/attrs.html> written by no one =
less than Glyph himself.

It=E2=80=99s still 100% free of magic but 100% full of convenience!

This version comes with two major new features I=E2=80=99d like to point =
out:


1. Attribute Metadata
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

There is a much nicer way to extend attrs now by using attribute =
metadata.  If you=E2=80=99re thinking Golang=E2=80=99s struct tags, =
it=E2=80=99s close!

However instead of exposing them to the users, it=E2=80=99s much nicer =
to *wrap* attrs and use metadata to bring the declarative approach to =
new areas.

For example this code will automatically load its configuration from env =
variables (as per 12Factor App: <https://12factor.net/config>):

```
@app_config(prefix=3D"APP", vault_prefix=3D"WHOIS_{env}")
class WhoisConfig:
    @app_config
    class Prometheus:
        address =3D env_var(default=3D"127.0.0.1")
        port =3D env_var(default=3D"0")
        consul_token =3D env_var_from_vault()

    env =3D env_var()
    prometheus =3D env_var_group(Prometheus)


if __name__ =3D=3D '__main__':
    ac =3D environ_to_app_config(WhoisConfig)

    print(ac)
```

Running it gives you:

```
$ env APP_ENV=3Ddev APP_PROMETHEUS_PORT=3D7000 =
SECRET_WHOIS_DEV_APP_PROMETHEUS_CONSUL_TOKEN=3Dabc python app.py
WhoisConfig(env=3D'dev', prometheus=3DPrometheus(address=3D'127.0.0.1', =
port=3D'7000', consul_token=3D'abc'))
```

(If you=E2=80=99re interested in the implementation of app_config, =
env_var, env_var_from_vault, env_var_group, and environ_to_app_config, =
have a look at =
<https://gist.github.com/hynek/78fef47fea3cbc6b683cd8ab0fb68567> =E2=80=93=
 it=E2=80=99s 87 LoC including empty lines.  I may or may not release a =
PyPI package one day)


2. Post Initialization Hooks
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

This is an often requested feature (just look at all those enthusiastic =
bikeshed painters:  <https://github.com/hynek/attrs/issues/68>) and =
allows you to define code that runs after the generated __init__ method.

This should make life easier when subclassing third party classes or if =
you want to derive attributes from others.


Full Changelog
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

-   Attributes now can have user-defined metadata which greatly improves =
attrs's extensibility. #96
-   Allow for a __attrs_post_init__ method that -- if defined -- will =
get called at the end of the attrs-generated __init__ method. #111
-   Add @attr.s(str=3DTrue) that will optionally create a __str__ method =
that is identical to __repr__. This is mainly useful with Exceptions and =
other classes that rely on a useful __str__ implementation but overwrite =
the default one through a poor own one. Default Python class behavior is =
to use __repr__ as __str__ anyways.

    If you tried using attrs with Exceptions and were puzzled by the =
tracebacks: this option is for you.
-   Don't overwrite __name__ with __qualname__ for attr.s(slots=3DTrue) =
classes. #99


Links
=3D=3D=3D=3D

PyPI: <https://pypi.org/project/attrs/>
Documentation: <http://attrs.org/>
GitHub: <https://github.com/hynek/attrs>

Cheers,
Hynek=