title: Boto3 Cloudformation Error: Template format error: unsupported structure
body: <p>I am unable to load parameters into the python boto3 Cloudformation client.</p>
  
  <p>Below is my parameter file:</p>
  
  <pre class="lang-json prettyprint-override"><code>[
    {"ParameterKey": "pVpcId",   "ParameterValue": "vpc-XXXXXX"},
    {"ParameterKey": "pContact", "ParameterValue": "XDXDXX"},
    {"ParameterKey": "pCC",      "ParameterValue": "XXXXX" },
    {"ParameterKey": "pFormat",  "ParameterValue": "True"}
  ]
  </code></pre>
  
  <p>I'm loading it into the program in the following way:</p>
  
  <pre class="lang-python prettyprint-override"><code>    with open(parameter_file, 'r') as infile:
          parameters=ast.literal_eval(infile.read())
          client = boto3.client('cloudformation',aws_access_key_id=access_key,aws_secret_access_key=secret_key,aws_session_token=session_token,region_name=region)
  
          response = client.create_stack(
              StackName=stack_name,
              TemplateURL=stack_url,
              Parameters=parameters
          )
  </code></pre>
  
  <p>When I establish a boto3 client with Cloudformation and call it, I get the error described below. The call works without the parameters, so it's definitely something to do with the parameter file.</p>
  
  <pre class="lang-none prettyprint-override"><code>    Traceback (most recent call last):
      File "cf_create_stack", line 85, in &lt;module&gt;
          Parameters=parameters
      File "/usr/lib/python2.7/site-packages/botocore/client.py", line 357, in _api_call
          return self._make_api_call(operation_name, kwargs)
      File "/usr/lib/python2.7/site-packages/botocore/client.py", line 661, in _make_api_call
          raise error_class(parsed_response, operation_name)
      botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the CreateStack operation: Template format error: unsupported structure.
  </code></pre>