title: Flask request.files is empty
body: <p>much like <a href="https://stackoverflow.com/questions/25589649/why-request-files-is-empty">this question</a>, I'm trying to follow the <a href="http://flask.pocoo.org/docs/0.12/patterns/fileuploads/" rel="noreferrer">simple Flask tutorial</a> for file upload to a flask server. In my specific case, I'm trying to upload an XML file.</p>
  
  <p>The (simplified) HTML I'm using is:</p>
  
  <pre><code>&lt;form action="" method="post" enctype="multipart/form-data"&gt;
      &lt;input type="file"&gt;
      &lt;input type="submit" value="Let's go!"&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>The request is correctly handled by a <code>if request.method == 'POST':</code> block, so I put in some print statements to troubleshoot:</p>
  
  <pre><code>print('request.method', request.method)
  print('request.args', request.args)
  print('request.form', request.form)
  print('request.files', request.files)
  </code></pre>
  
  <p>and the result was the following:</p>
  
  <pre><code>request.method POST
  request.args ImmutableMultiDict([])
  request.form ImmutableMultiDict([])
  request.files ImmutableMultiDict([])
  </code></pre>
  
  <p>What am I doing wrong? I can provide more complete source code if needed.</p>