YAML 解析为对象 (PyYAML Python3)

我有以下代码：

class Settings:
    def __init__(self, annual_volatility_target):
        self.annual_volatility_target = annual_volatility_target
        self.daily = annual_volatility_target/np.sqrt(252)

def yaml_load(name):
    with open('yaml/' + str(name) + '.yaml', 'r') as ymlfile:
        return yaml.load(ymlfile)

settings = yaml_load("settings")

使用以下 YAML：

!!python/object:v.Settings
annual_volatility_target: 0.25

问题是，当我加载时settings, settings.daily未设置。settings.annual_volatility_target是，无论我是否这么说__init__ or not.

如果我实例化一个Settings手动对象（即不使用 PyYAML），它工作正常。

我究竟做错了什么？

PyYAML 中的 Python 对象是通过两步过程构建的。第一的__new__被称为（在Constructor.make_python_instance()）然后设置属性（在Constructor.set_python_instance_state()）。需要这两个步骤的过程是因为 YAML 支持对对象的引用，并且如果该对象是（间接）自引用的，则无法一次性构造它，因为它所依赖的参数（包括其自身）尚不可用。

您可以通过两种方式解决这个问题。您可以定义__setstate__() for Settings这将被称为dict并从__init__()还有：

import yaml

yaml_str = """\
!!python/object:try.Settings
annual_volatility_target: 0.25
"""

class Settings:
    def __init__(self, annual_volatility_target):
        self.__setstate__({annual_volatility_target: annual_volatility_target})

    def __setstate__(self, kw):
        self.annual_volatility_target = kw.get('annual_volatility_target')
        self.daily = self.annual_volatility_target/np.sqrt(252)

    def __repr__(self):
        return "Setting({}, {})".format(self.annual_volatility_target, self.daily)

settings = yaml.load(yaml_str)

print(settings)

另一个更通用（非 PyYAML）的解决方案是创建daily第一次访问时的值：

class Settings:
    def __init__(self, annual_volatility_target):
        self.annual_volatility_target = annual_volatility_target

    @property:
    def daily(self):
         return annual_volatility_target/np.sqrt(252)

如果您访问daily通常，那么您应该将其缓存在例如self._daily第一次计算该值时：

class Settings:
    def __init__(self, annual_volatility_target):
        self.annual_volatility_target = annual_volatility_target
        self._daily = None

    @property:
    def daily(self):
         if self._daily is None:  
             self._daily = annual_volatility_target/np.sqrt(252)
         return self._daily