YAML解析为对象(PyYAML Python3)
作者:互联网
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,当我加载设置时,settings.daily未设置. settings.annual_volatility_target是,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),它可以正常工作.
我究竟做错了什么?
解决方法:
PyYAML中的Python对象分两步构建.首先调用__new__(在Constructor.make_python_instance()中),然后设置属性(在Constructor.set_python_instance_state()中).这个两步过程是必需的,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,则它不能一次构造,因为它依赖的参数(包括它自己)尚不可用.
您可以通过两种方式解决此问题.您可以为Settings定义__setstate __(),并使用dict调用它,并从__init __()调用它:
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)
另一个更通用的(非PyYAML)解决方案是在首次访问时创建每日价值:
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)
如果您经常每天访问,那么您应该将其缓存在例如self._daily第一次计算值时:
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
标签:python,pyyaml 来源: https://codeday.me/bug/20190706/1395415.html