docs: def sentiment(
      text       = None,
      confidence = False
      ):
      """
      This function accepts a string text input. It calculates the sentiment of
      the text, "pos" or "neg". By default, it returns this calculated sentiment.
      If selected, it returns a tuple of the calculated sentiment and the
      classificaton confidence.
      """
      try:
          words = text.split(" ")
          # Remove empty strings.
          words = [word for word in words if word]
          features = word_features(words)
          classification = classifier.classify(features)
          confidence_classification = classifier.prob_classify(features).prob(classification)
      except:
          classification = None
          confidence_classification = None
      if confidence:
          return (
              classification,
              confidence_classification
          )
      else:
          return classification