title: django-widget-tweaks with django custom tags
body: <p>I am using django-widget-tweaks to render my django form fields.</p>
  
  <p>Now I need to show the return value of a custom django tag as the value of my render field.</p>
  
  <p>This is my template tag</p>
  
  <pre><code>from forex_python.bitcoin import BtcConverter
  
  @register.simple_tag
  def btc_price_in_sgd():
      coin_obj = BtcConverter()
      price = coin_obj.get_latest_price('SGD')
      return price
  </code></pre>
  
  <p>I used the return value of this filter as my form input field</p>
  
  <p>here is the code I used to show in template</p>
  
  <pre><code>{% render_field exchange_form.price class="form-control" value=btc_price_in_sgd %}
  </code></pre>
  
  <p>but this is not working</p>