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，因为我使用验证模板测试了它们:

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

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

然而，当我尝试使用 PyYAML 库读取它们时，出现如下错误:

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

无法确定标记!Sub"的构造函数

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

和其他人.

举例来说，我尝试使用这个 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'))

导致:

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

如何使用 PyYAML 等库解析 CloudFormation YAML 文件?

推荐答案

可以使用 cfn_tools 库，随 aws 一起提供-cfn-template-flip 项目.

It is possible to use the cfn_tools library that ships with the aws-cfn-template-flip project.

安装库:

▶ pip install cfn_flip

那么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))

这个库并没有真正被记录下来，但其中也有各种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.

这篇关于使用 PyYAML 库解析 AWS CloudFormation 模板的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！