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.

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