title: Append header in flask request
body: <p>i am using python flask in my application. I want to change the header before each request in order to add information for zipkin distributed tracing. My current code looks like:</p>
  
  <pre><code>@app.before_request
  def before_request():
      headers={}
      headers.update(zipkin.create_http_headers_for_new_span())
      request.headers.append(headers)
  </code></pre>
  
  <p>Unfortunately, this is not working as the method <em>append</em> does not exist. What is the right approach?</p>
  
  <p>Best regards
  Martin</p>