title: Python: Iterate Over Dictionary that Contains Lists and Store the Keys and Values in a String
body: <pre><code>params={
      'key1': 'value1',
      'key2': ['value_a','value_b']
  }
  </code></pre>
  
  <p>This is what I'm starting with but it can't handle the list.</p>
  
  <pre><code>str_params = ''
  for key, value in params.items():
      print (key,value)
      str_params += '&amp;' + key + '=' + value
  </code></pre>
  
  <p>I'm trying to yield this string. </p>
  
  <pre><code>str_params = '&amp;key1=value1&amp;key2=value_a&amp;key2=value_b'     
  </code></pre>