title: Append return values to list in Robot Framework
body: <p>My test step creates 5 worker threads to upload a file to a server and returns the server HTTP response codes for each thread.
  I would like to append those to a list of response codes for each step. </p>
  
  <pre><code>TC001_Single_User_Upload
     [Documentation] Uploading single file by single user
     ${result}       single user test file upload    test_file.txt    test1   test
     Append To List  @{RESPONSE_LIST}    ${result}
     ${result}       single user test file upload    test_file.txt    test1   test
     Append To List  @{RESPONSE_LIST}    ${result}
     log variables
     log many     @{RESPONSE_LIST}
  </code></pre>
  
  <p>My current log files shows this :</p>
  
  <pre><code>20171127 13:59:01.911 - INFO - @{RESPONSE_LIST} = [ ]
  20171127 13:59:01.911 - INFO - @{result} = [ &lt;Response [201]&gt; | &lt;Response [201]&gt; | &lt;Response [201]&gt; | &lt;Response [201]&gt; | &lt;Response [201]&gt; ]
  </code></pre>
  
  <p>Q: why is my @{RESPONSE_LIST} empty?</p>