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July 23, 2020 16:54
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Enhanced python properties with some metaprog.
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| # file: objects.py | |
| # Copyright 2020 Frank David Martínez Muñoz (mnesarco) | |
| # License: MIT | |
| from typing import Union | |
| __all__ = ('self_properties', 'properties') | |
| def self_properties(self, scope: dict, exclude=(), save_args: bool = False): | |
| """Copies all items from `scope` to self as attributes with single underscore prefix. | |
| :param self: instance ref. | |
| :param scope: dictionary with attributes. | |
| :param exclude: tuple with names to exclude from `scope`. | |
| :param save_args: if True, sets self._args with a tuple with `(scope - exclude).values` | |
| """ | |
| if save_args: | |
| args = [] | |
| for (k, v) in scope.items(): | |
| if k != 'self' and k not in exclude: | |
| setattr(self, '_' + k, v) | |
| args.append(v) | |
| self._args = tuple(args) | |
| else: | |
| for (k, v) in scope.items(): | |
| if k != 'self' and k not in exclude: | |
| setattr(self, '_' + k, v) | |
| class properties: | |
| """ | |
| Utilities for building properties with extended features. | |
| """ | |
| __slots__ = ['_slots', '_scope', '_var', '_auto_dirty'] | |
| def __init__(self, scope: dict, var_name: str, auto_dirty: bool = False): | |
| self._slots = [] | |
| self._scope = scope | |
| self._var = var_name | |
| self._auto_dirty = auto_dirty | |
| def __enter__(self): | |
| return self | |
| def __exit__(self, exc_type, exc_val, exc_tb): | |
| # Export slots to scope | |
| slots = self._scope.get('__slots__', None) | |
| if slots is None: | |
| self._scope['__slots__'] = tuple(self._slots) | |
| elif isinstance(slots, list): | |
| self._scope['__slots__'] += self._slots | |
| elif isinstance(slots, tuple): | |
| self._scope['__slots__'] = (*self._scope['__slots__'], *self._slots) | |
| # Clean scope | |
| if self._var in self._scope: | |
| del self._scope[self._var] | |
| # Clean references | |
| self._scope = None | |
| self._slots = None | |
| self._var = None | |
| def prop(self, read_only: bool = False, listener: Union[bool, str] = None, auto_dirty=False): | |
| """Decorator: Generates a property with additional features. | |
| :param read_only: if True, only a getter is generated. | |
| :param listener: if str, changes will fire `self.[listener]`, if bool, changes will fire `self._changed` | |
| :param auto_dirty: if True, changes will set `self._is_dirty` | |
| :return: property. | |
| """ | |
| auto_dirty = self._auto_dirty or auto_dirty | |
| if auto_dirty and '_is_dirty' not in self._slots: | |
| self._slots.append('_is_dirty') | |
| def decorator(f): | |
| field = '_' + f.__name__ | |
| if read_only and listener: | |
| raise ValueError(f"property {field} cannot be read_only and observable at the same time.") | |
| self._slots.append(field) | |
| if read_only: | |
| setter = None | |
| else: | |
| if listener: | |
| listener_name = listener if isinstance(listener, str) else '_changed' | |
| def setter(inst, new): | |
| old = getattr(inst, field, None) | |
| if old != new: | |
| setattr(inst, field, new) | |
| if auto_dirty: | |
| inst._is_dirty = True | |
| (getattr(inst, listener_name))(field, old, new) | |
| else: | |
| def setter(inst, new): | |
| if getattr(inst, field, None) != new: | |
| setattr(inst, field, new) | |
| if auto_dirty: | |
| inst._is_dirty = True | |
| return property( | |
| lambda inst: getattr(inst, field, f(inst)), | |
| setter, | |
| None, | |
| f.__doc__ | |
| ) | |
| return decorator | |
| # Example usage: | |
| # | |
| # from objects import * | |
| # | |
| # class Car: | |
| # with properties(locals(), 'meta') as meta: | |
| # | |
| # @meta.prop(read_only=True) | |
| # def brand(self) -> str: | |
| # """Brand""" | |
| # | |
| # @meta.prop(read_only=True) | |
| # def max_speed(self) -> float: | |
| # """Maximum car speed""" | |
| # | |
| # @meta.prop(listener='_on_acceleration') | |
| # def speed(self) -> float: | |
| # "Speed of the car""" | |
| # return 0 # Default stopped | |
| # | |
| # @meta.prop(listener='_on_off_listener') | |
| # def on(self) -> bool: | |
| # """Engine state""" | |
| # return False | |
| # | |
| # def __init__(self, brand: str, max_speed: float = 200): | |
| # self_properties(self, locals()) | |
| # | |
| # def _on_off_listener(self, prop, old, on): | |
| # if on: | |
| # print(f"{self.brand} Turned on, Runnnnnn") | |
| # else: | |
| # self._speed = 0 | |
| # print(f"{self.brand} Turned off.") | |
| # | |
| # def _on_acceleration(self, prop, old, speed): | |
| # if self.on: | |
| # if speed > self.max_speed: | |
| # print(f"{self.brand} {speed}km/h Bang! Engine exploded!") | |
| # self.on = False | |
| # else: | |
| # print(f"{self.brand} New speed: {speed}km/h") | |
| # else: | |
| # print(f"{self.brand} Car is off, no speed change") | |
| # | |
| # | |
| # mycar = Car('Ford') | |
| # | |
| # # Car is turned off | |
| # for speed in range(0, 300, 50): | |
| # mycar.speed = speed | |
| # | |
| # # Car is turned on | |
| # mycar.on = True | |
| # for speed in range(0, 350, 50): | |
| # mycar.speed = speed |
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