使用PyYAML库解析AWS CloudFormation模板 [英] Parse an AWS CloudFormation template with the PyYAML library

问题描述

我正在使用需要读取AWS CloudFormation YAML模板的PyYAML库编写自定义Python应用程序。

I am writing a custom Python application using the PyYAML library that needs to read in AWS CloudFormation YAML templates.

我知道模板是有效的CloudFormation模板，因为我使用validate-template测试了它们：

I know the templates are valid CloudFormation templates, because I tested them using validate-template:

▶ aws cloudformation validate-template --template-body file://cloudformation.yml

但是，当我尝试使用PyYAML库读取它们时，像这样的错误：

When I try to read them using the PyYAML library, however, I get errors like:

yaml.scanner.ScannerError：此处不允许映射值

yaml.scanner.ScannerError: mapping values are not allowed here

和

无法确定标签！Sub的构造函数

could not determine a constructor for the tag "!Sub"

等。

通过示例，我尝试以下AWS示例模板：

By way of example, I try this AWS example template:

▶ curl -s \
    https://raw.githubusercontent.com/awslabs/aws-cloudformation-templates/master/aws/services/CloudFormation/FindInMap_Inside_Sub.yaml \
    -o FindInMap_Inside_Sub.yaml

然后：

▶ python
Python 2.7.15 (default, Nov 27 2018, 21:40:55) 
[GCC 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import yaml
>>> yaml.load(open('FindInMap_Inside_Sub.yaml'))

这会导致：

yaml.constructor.ConstructorError: could not determine a constructor for the tag '!FindInMap'
  in "FindInMap_Inside_Sub.yaml", line 89, column 45

如何解析CloudFormation YAML

推荐答案

是否可以使用 cfn_tools 随 aws-cfn-template-flip 项目。

安装该库：

▶ pip install cfn_flip

然后在模板中读取的最简单的Python可能是：

Then the simplest Python to read in the template might be:

#!/usr/bin/env python

import yaml
from cfn_tools import load_yaml, dump_yaml

text = open('./FindInMap_Inside_Sub.yaml').read()
data = load_yaml(text)

print dump_yaml(data)

该库并未真正记录，但是其中还有许多方法可以自定义值得探索的输出格式。

This library is not really documented but there are also various methods in there for customising the formatting of the output worth exploring.

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