Question

我已获得以下代码：

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settings时，settings.daily未设置。 settings.annual_volatility_target是__init__，无论我是否在Settings中这么说。

如果我手动实例化JsonObject obje = new JsonObject(); obje.addProperty("id","a"); obje.addProperty("NUMERO", 3); mClient.getTable("deneme").insert(obje);对象（即不使用PyYAML），它可以正常工作。

我做错了什么？

Answer 1

一种可能性是为Settings写一个constructor：

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)

我必须使用修改后的yaml文件（我无法使其与注释!!python/object:v.Settings一起使用）：

!v.Settings
annual_volatility_target: 0.25

Answer 2

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，如果该对象是（间接）自引用的，它不能一次构造，因为它所依赖的参数（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__setstate__()定义Settings，并使用dict调用__init__()，并从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)调用此内容：

daily

另一种更通用的（非PyYAML）解决方案是在首次访问时创建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)值：

daily

如果您经常访问self._daily，那么您应该将其缓存在例如{0}中第一次计算值时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：

<?php
header("content-type: image/png");
$qr_image = imagecreatefrompng("https://chart.googleapis.com/chart?chs=177x177&cht=qr&chl=MyHiddenCode&choe=UTF-8"); //no need for file_get_contents
$save = getcwd()."/temp/chart123.png";
imagepng($qr_image,$save); //save the file to $save path
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YAML解析为对象（PyYAML Python3）

2 个答案: