YAML解析到

Question

我有下面的代码对象（PyYAML Python3）：

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") 

用下面的YAML：

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

的问题是，当我加载settings，settings.daily ISN” t集。无论我是否在__init__中这么说。

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

我在做什么错？

Answer 1

的Python PyYAML中的对象是在两个步骤中构建的。首先调用__new__（在Constructor.make_python_instance()中），然后设置属性（在Constructor.set_python_instance_state()中）。由于YAML支持对对象的引用，并且该对象（间接）是自引用，所以它不能一次构建，因为YAML所依赖的参数（包括它本身）尚不可用。

你可以用两种方法解决这个问题。您可以为Settings定义__setstate__()，这将有dict被调用，从__init__()称之为还有：

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) 

另外，和更普遍的（非PyYAML）的解决方案是在第一次访问创建daily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) 

如果您经常访问daily，那么您应该将它缓存在eg self._daily你第一次计算值：

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 

Answer 2

一种可能性是写一个constructor为Settings：

import yaml 
import numpy as np 

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(str(name) + '.yaml', 'r') as ymlfile: 
     return yaml.load(ymlfile) 

def settings_constructor(loader, node): 
    fields = loader.construct_mapping(node) 
    return Settings(fields['annual_volatility_target']) 

yaml.add_constructor('!v.Settings', settings_constructor) 

settings = yaml_load("settings") 

print(settings.annual_volatility_target) 
print(settings.daily) 

我必须使用修改yaml文件（我无法使其与标注!!python/object:v.Settings工作）：

!v.Settings 
annual_volatility_target: 0.25