aspect oriented programming helper
pip install concerns==1.0
Python implementation of the Ruby’s ActiveSupport::Concern behavior.
Note: the class context is the fourth argument of the
metaclass __init__
method,
formally “namespace”:
def __init__(cls, name: str, bases: tuple, namespace: dict) -> None:
...
It is a dictionary representation of the class body.
If the aspect is a class, its context will be merged to the target context on its factoring.
from typing import NamedTuple
from concerns import concern
class SerialMixin:
def serialize(self) -> str:
return json.dumps(self._asdict(), sort_keys=True)
@classmethod
def deserialize(cls, data: str):
return cls(**json.loads(data))
class PersonBase(NamedTuple):
name: str
surname: str
class Person(PersonBase):
concern(SerialMixin)
If the aspect is a mapping (a dictionary, by example), it itself will be merged to the target context on its factoring.
from concerns import concern
class Animal:
# Too simple use, avoid doing it
concern({voice='grrr'})
def __init__(self, *, voice: str = None):
if voice:
self.voice = voice
def say(self) -> None:
print(self.voice)
If the aspect is a callable, the target class context will be passed as parameter to the aspect for processing before its factoring.
from concerns import concern
from collections.abc import MutableMapping
from datetime import datetime
def make_timed(context: MutableMapping) -> None:
"""
Reusable aspect function to add creating time to objects
"""
def set_created_attr(attr: str) -> None:
context[attr] = None
def new(cls, name: str, bases: tuple, _dict: dict):
self = super().__new__(cls, name, bases, _dict)
setattr(self, attr) = datetime.now()
return self
context['__new__'] = new
context['set_created_attr'] = set_created_attr
class Register:
concern(make_timed)
... # more class attributes
set_created_attr('created_at')