title: pyyaml yaml.load returns str instead of dict
body: <p>Using pyyaml and python3, the following in-memory yaml string loads without error but yaml.full_load() returns a str and not a dict. Is this expected behavior? Thanks.</p>
  
  <pre><code>main:
    orgs:
      &amp;org1 org1:
        categories:
          - one
          - two
          - three
      &amp;org2 org2:
        categories:
          - one
          - two
    people:
      - userid: user1
        org: *org1
        roles:
          - roleA
          - roleB
      - userid: user2
        org: *org2
        roles:
          - roleA
  </code></pre>
  
  <pre><code>print("MAIN_YAML = " + os.getenv("MAIN_YAML"))
  
  try:
      MAIN_YAML = yaml.full_load(os.getenv("MAIN_YAML"))
      print("PARSED SUCCESSFULLY")
      print(isinstance(MAIN_YAML, dict))
      print(type(MAIN_YAML))
  except (yaml.YAMLError, yaml.YAMLLoadWarning) as e:
      print(e)
  </code></pre>
  
  <pre><code>MAIN_YAML = main:orgs:&amp;org1org1:categories:-one-two-three&amp;org2org2:categories:-one-twopeople:-userid:user1org:*org1roles:-roleA-roleB-userid:user2org:*org2roles:-roleA
  PARSED SUCCESSFULLY
  False
  &lt;class 'str'&gt;
  
  </code></pre>
  
  <p>Here's the shell script that creates the one-liner:</p>
  
  <pre><code>tr -d '\n\t' &lt; main.yaml &gt; temp.yaml
  tr -d ' ' &lt; temp.yaml &gt; main_squeezed.yaml
  MAIN_YAML=$(cat main_squeezed.yaml)
  </code></pre>