Function dump_yaml sometimes converted string values to number values, causing invalid CFN templates

[canhnt]

Description

When parsing YAML files containing string scalar longer than 8 chars and start with 0, the function dump_yaml strips single (and double) quotes, which converts string scalar to number scalar. When CFN templates refers these string values in Ref or Sub functions, it causes template error.

Use-case '012345678'

Reproduction script:

import cfn_tools
content = "Parameters:\n  MyAccountId:\n    Type: String\n    Default: '012345678'"
body = cfn_tools.load_yaml(content)
template_body = cfn_tools.dump_yaml(body)
print template_body

Expected output:

Parameters:
  MyAccountId:
    Type: String
    Default: '012345678'

Actual output:

Parameters:
  MyAccountId:
    Type: String
    Default: 012345678

Use-case '01234567'

import cfn_tools
content = "Parameters:\n  MyAccountId:\n    Type: String\n    Default: '01234567'"
body = cfn_tools.load_yaml(content)
template_body = cfn_tools.dump_yaml(body)
print template_body

Output:

Parameters:
  MyAccountId:
    Type: String
    Default: '01234567'

[canhnt]

Close the issue because the bug is for https://github.com/awslabs/aws-cfn-template-flip