Python 生成对象或对象列表的对象工厂
我有以下代码:Python 生成对象或对象列表的对象工厂,python,object,factory,Python,Object,Factory,我有以下代码: def f(cls, value): # cls is a class # value is a string value if cls == str: pass # value is already the right type elif cls == int: value = int(value) elif cls == C1: value = C1(value) elif cls == C2: value = C2(v
def f(cls, value):
# cls is a class
# value is a string value
if cls == str:
pass # value is already the right type
elif cls == int:
value = int(value)
elif cls == C1:
value = C1(value)
elif cls == C2:
value = C2(value)
elif cls == C3
# in this case, we convert the string into a list of objects of class C3
value = C3.parse(value)
else
raise UnknownClass(repr(cls))
return value
显然,我正试图用以下内容来取代它:
def f(cls, value)
return cls(value)
不幸的是,在某些情况下(如果cls==C3),对输入的解析会导致该类的对象列表,而不仅仅是一个对象。处理这个问题的好方法是什么?我可以访问所有的类。这取决于你如何处理列表。这是最简单的方法: obj=cls(值) 如果类型(obj)=列表: 句柄列表(obj) 返回obj 如果大多数情况下最好通过调用
cls来处理,而少数情况下最好通过其他方式处理,最简单的方法是选择后者:
themap = {C3: C3.parse}
for C in (str, C1, C2):
themap[C] = C
def f(cls, value):
wot = themap.get(cls)
if wot is None:
raise UnknownClass(repr(cls))
return wot(value)
请注意,在字符串上调用str
是一个非常快速的步骤,因此为了代码的简单性,通常值得避免“单独选择”特定的情况。我假设@max在编写类X
时,无法从X()返回X列表,而只返回X,您可以覆盖X.\uuuuuuuuuuuuuuuuuuuu
以返回您想要的任何内容(如果不是X
实例,X.\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu,但是非常不方便classmethod
通常是构建“备用”构造函数的更好方法。最好使用isinstance内置方法,而不是使用类型!