code: def validate_yaml(yaml_in, yaml_fn):
      
      try:
          import yamllint.linter as linter
          from yamllint.config import YamlLintConfig
      except ImportError:
          return
      conf = """{"extends": "relaxed",
                 "rules": {"trailing-spaces": {"level": "warning"},
                           "new-lines": {"level": "warning"},
                           "new-line-at-end-of-file": {"level": "warning"}}}"""
      if utils.file_exists(yaml_in):
          with open(yaml_in) as in_handle:
              yaml_in = in_handle.read()
      out = linter.run(yaml_in, YamlLintConfig(conf))
  
      for problem in out:
          msg = '%(fn)s:%(line)s:%(col)s: [%(level)s] %(msg)s' % {'fn': yaml_fn,
                                                                  'line': problem.line,
                                                                  'col': problem.column,
                                                                  'level': problem.level,
                                                                  'msg': problem.message}
          if problem.level == "error":
              raise ValueError(msg)
docs: Check with yamllint the yaml syntaxes
      Looking for duplicate keys.