cfn-yaml-tags

Python support for CloudFormation YAML tags

In CloudFormation YAML, references can be made as an object:

SomeKey: {Ref: SomeResourceId}

or using YAML tags:

SomeKey !Ref SomeResourceId

However, these are custom YAML tags, and can't be parsed by PyYAML out of the box.

cfn_yaml_tags implements this support. Importing the cfn_yaml_tags module will add them to the PyYAML library so that you can use load and dump with them.

By default, they are not added to the safe_load and safe_dump methods. Call the mark_safe() method to add it to these methods.

It also provides a JSONEncoder subclass, JSONFromYAMLEncoder, to enable writing out JSON from templates loaded from YAML that have the tags.

Usage:

import yaml
import cfn_yaml_tags

doc = """
Resources:
  MyBucket:
    Type: AWS::S3::Bucket
    Properties: {}
  MyFunction:
    Type: AWS::Lambda::Function
    Properties:
      Environment:
        BucketName: !Ref MyBucket
        # etc.
"""

template = yaml.load(doc)

# optional:
# cfn_yaml_tags.mark_safe()
# template = yaml.safe_load(doc)

yaml_doc = yaml.dump(template)

json_doc = cfn_yaml_tags.JSONFromYAMLEncoder().encode(template)
"""