1import yaml 2from yaml import ScalarNode, SequenceNode 3from six import string_types 4 5# This helper copied almost entirely from 6# https://github.com/aws/aws-cli/blob/develop/awscli/customizations/cloudformation/yamlhelper.py 7 8 9def yaml_parse(yamlstr): 10 """Parse a yaml string""" 11 yaml.SafeLoader.add_multi_constructor("!", intrinsics_multi_constructor) 12 return yaml.safe_load(yamlstr) 13 14 15def intrinsics_multi_constructor(loader, tag_prefix, node): 16 """ 17 YAML constructor to parse CloudFormation intrinsics. 18 This will return a dictionary with key being the instrinsic name 19 """ 20 21 # Get the actual tag name excluding the first exclamation 22 tag = node.tag[1:] 23 24 # Some intrinsic functions doesn't support prefix "Fn::" 25 prefix = "Fn::" 26 if tag in ["Ref", "Condition"]: 27 prefix = "" 28 29 cfntag = prefix + tag 30 31 if tag == "GetAtt" and isinstance(node.value, string_types): 32 # ShortHand notation for !GetAtt accepts Resource.Attribute format 33 # while the standard notation is to use an array 34 # [Resource, Attribute]. Convert shorthand to standard format 35 value = node.value.split(".", 1) 36 37 elif isinstance(node, ScalarNode): 38 # Value of this node is scalar 39 value = loader.construct_scalar(node) 40 41 elif isinstance(node, SequenceNode): 42 # Value of this node is an array (Ex: [1,2]) 43 value = loader.construct_sequence(node) 44 45 else: 46 # Value of this node is an mapping (ex: {foo: bar}) 47 value = loader.construct_mapping(node) 48 49 return {cfntag: value} 50