title: Checking inputs of form in django before submit
body: <p>I am using Django and try to submit a form.
  I have a "call-us" form and there is 3 fields.
  I want to make this, If one of the fields is empty, and the user clicked on Submit button, don't send the info to View and warm the user that they must complete the required fields.</p>
  
  <p>here is my form:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;form role="form" action="{% url "landingpages:callusthanks" %}" method="post" style="max-width: 500px;margin: 0 auto;margin-top: 30px;"&gt;
      {% csrf_token %}
      &lt;div class="form-group"&gt;
          &lt;div class="input-group"&gt;
              &lt;div class="input-group-addon"&gt;&lt;i class="fa fa-user"&gt;&lt;/i&gt;&lt;/div&gt;
              &lt;input type="text"  name="name" class="form-control" id="name" placeholder="Name"&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;div class="form-group"&gt;
          &lt;div class="input-group"&gt;
              &lt;div class="input-group-addon"&gt;&lt;i class="fa fa-at"&gt;&lt;/i&gt;&lt;/div&gt;
              &lt;input type="text" name="email" id="email" class="form-control" placeholder="Email"&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;div class="form-group"&gt;
          &lt;div class="input-group"&gt;
              &lt;div class="input-group-addon"&gt;&lt;i class="fa fa-envelope-o"&gt;&lt;/i&gt;&lt;/div&gt;
              &lt;textarea name="message" class="form-control" id="message" placeholder="Message"&gt;&lt;/textarea&gt;
          &lt;/div&gt;
      &lt;/div&gt;
      &lt;div class="form-group row"&gt;
          &lt;div class="col-xs-6 col-xs-offset-6"&gt;
              &lt;button type="submit" class="form-control"&gt;Send&lt;/button&gt;
          &lt;/div&gt;
      &lt;/div&gt;
  &lt;/form&gt;</code></pre>
  </div>
  </div>
  </p>