An alternative API for creating attrs fields
Project description
Elysia
Elysia is an addon for attrs that provides an alternative API for creating fields on
@define
d classes.
Installation
pip install elysia
Usage
Elysia's sole export is the Fields
class, which wraps attrs.field
, attrs.setters
, and attrs.validators
to
provide a more concise API for defining instance attributes.
Here's a brief example of a class created with attrs and Elysia:
from datetime import datetime
from attrs import define
from elysia import Fields
@define
class User:
name: str = Fields.field()
password: str = Fields.field(
on_setattr=Fields.setters.validate,
validator=Fields.validators.min_len(8)
)
created_at: datetime = Fields.attr(factory=datetime.utcnow, frozen=True)
The User
class has two __init__
arguments: name
and password
. Whenever set, password
is validated to
ensure it's at least 8 characters long.
User
also has a created_at
attribute that can't set via an __init__
argument. When a User
object is
instantiated, created_at
is set to the current time and cannot be changed afterwards.
So...how does all that work, exactly?
Glad you asked.
There are two ways to define an attribute with Elysia: Fields.field()
and Fields.attr()
. Fields.field()
defines
attributes that map to __init__
arguments; Fields.attr()
defines attributes that do not. Both are wrappers around
attrs.field
and accept all the same arguments. Like attrs.field
, all arguments to Fields.field()
and Fields.attr()
are keyword-only.
Both methods also accept an optional, boolean, frozen
argument. Setting it to True
is a shortcut
for on_setattr=attrs.setters.frozen
— that is, it freezes the attribute, raising an exception if you try to set it
after initialization.
Warning
Elysia is happy to combine
frozen=True
with anything else you pass toon_setattr
, butattrs.setters.frozen
will be applied first, which may not be what you expect.
Fields also provides access to attrs' setters and validators via Fields.setters
and Fields.validators
,
respectively. It makes no difference whether setters and validators are accessed through Fields
or attrs
. Do what
you like.
License
Elysia is licensed under the MIT License.
Project details
Download files
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.