title: how I check in flask that field from form was filled by user
body: <p>I don't know how to check if user fill field in form in flask.</p>
  
  <p>I have this form</p>
  
  <pre><code>&lt;form method="POST" class="form-horizontal"&gt;
     &lt;input type="text" name="name" value="{{ name }}"&gt;
     &lt;input type="submit" class="btn" value="Add"/&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>then I want check value in field and process it.</p>
  
  <pre><code>if request.method == 'POST':
      name = request.form['name']
      if name is None:  // this doesn't work
          # do something
      if name == string.empty: // this also doesn't work
          # do something
  </code></pre>
  
  <p>Please could you give me some advise.
  Thanks</p>