相关疑难解决方法(0)

有没有办法在Python中创建类级别的只读属性？例如,如果我有课Foo,我想说:

x = Foo.CLASS_PROPERTY

但是阻止任何人说:

Foo.CLASS_PROPERTY = y

编辑: 我喜欢Alex Martelli解决方案的简单性,但不喜欢它需要的语法.他和~ututbu的答案都启发了以下解决方案,这更接近我所寻找的精神:

class const_value (object):
    def __init__(self, value):
        self.__value = value

    def make_property(self):
        return property(lambda cls: self.__value)

class ROType(type):
    def __new__(mcl,classname,bases,classdict):
        class UniqeROType (mcl):
            pass

        for attr, value in classdict.items():
            if isinstance(value, const_value):
                setattr(UniqeROType, attr, value.make_property())
                classdict[attr] = value.make_property()

        return type.__new__(UniqeROType,classname,bases,classdict)

class Foo(object):
    __metaclass__=ROType
    BAR = const_value(1)
    BAZ = 2

class Bit(object):
    __metaclass__=ROType
    BOO = const_value(3)
    BAN = 4

现在,我得到:

Foo.BAR …

在python中,有没有办法防止在定义对象后添加新的类变量？

例如:

class foo:
    def __init__(self):
        self.a = 1
        self.b = 2
        self.c = 3

bar = foo()
try:
    bar.d = 4
except Exception, e:
    print "I want this to always print"

或者,有没有办法计算对象中的变量数？

class foo:
    def __init__(self):
        self.a = 1
        self.b = 2
        self.c = 3
    def count(self):
        ...

bar = foo()
if bar.count() == 3:
    print "I want this to always print"

我想到这样做的唯一方法是使用字典或列表:

class foo:
    def __int__(self):
        self.dict = {'foo':1, 'bar':2} 
        self.len  = 2
    def chk():
        return self.len == …