[英]How to call a baseclass function whenever a certain method is called in derived class in python?
我正在像python中定義一個基類
class Base(object):
def __init__(self):
self._changed = False
和一些派生類:
class Car(Base):
def set_type(self, type_):
# do something
def set_mileage(self, mileage):
# do something
class Flower(base):
def set_name(self, name):
# do something
在此示例中,我現在想在調用派生類之一的set
方法時將屬性'_changed'設置為True
。 我可以添加行
self._changed = True
每個set
方法或使用裝飾器,但是我正在尋找一種更方便,更自動的方法,只要調用以'set_'開頭的方法即可。 我正在考慮使用__getattribute__
如以下未嘗試過(且無法正常工作的示例):
def __getattribute__(self, name):
if name.startswith('set_'):
self._changed = True
return self.__getattribute__(name)
那么如何以正確的方式實現呢?
更新:這是一個完全正常的示例,這次使用帶有setter和getter的元類和描述符:
class Field(object):
def __get__(self, ins, type):
return getattr(ins, self.field_name, None)
def __set__(self, ins, val):
setattr(ins, self.field_name, val)
ins._changed = True
class Meta(type):
def __new__(cls, clsname, bases, dct):
for k, v in dct.items():
if isinstance(v, Field):
v.field_name = '_' + k
return type.__new__(cls, clsname, bases, dct)
class Base(object):
__metaclass__ = Meta
def __init__(self):
self._changed = False
class Car(Base):
type = Field()
mileage = Field()
class Flower(Base):
name = Field()
演示:
>>> c = Car()
>>> c._changed
False
>>> c.type = "4X4"
>>> c._changed
True
>>> c1 = Car()
>>> c1._changed
False
>>> c1.mileage = 100
>>> c1._changed
True
>>> c.type
'4X4'
>>> c1.mileage
100
>>> f = Flower()
>>> f._changed
False
>>> f.name = "Rose"
>>> f._changed
True
>>> f.name
'Rose'
我會為此使用裝飾器。 像這樣的東西(未經測試):
def isGet(func):
def newFunc(self, var):
self._changed = True
func(self, var)
return
return newFunc
然后,在任何需要此行為的get方法中,您只需
@isGet
def set_mileage(self, mileage):
# dosomething
元類將在這里工作:
from types import FunctionType
from functools import wraps
class Setter(type):
def __new__(cls, clsname, bases, dct):
for item in dct:
if item.startswith("set_") and isinstance(dct[item], FunctionType):
dct[item] = cls.changer(dct[item])
return super(Setter, cls).__new__(cls, clsname, bases, dct)
@staticmethod
def changer(func):
@wraps(func)
def wrapper(self, *args, **kwargs):
self._changed = True
return func(self, *args, **kwargs)
return wrapper
class Base(object):
__metaclass__ = Setter
def __init__(self):
self._changed = False
然后像往常一樣從Base繼承。
用法示例:
>>> from meta import Car
>>> c = Car()
>>> c._changed
False
>>> c.set_type("blah")
ok
>>> c._changed
True
元類只是自動修飾類的__dict__
中以set_
開頭的任何方法。
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