def word_split(phrase, list_of_words, output=None):
    if output is None:
        output = []

    for word in list_of_words:
        if phrase.startswith(word):
            output.append(word)
            return word_split(phrase[len(word):], list_of_words, output)
    return output

print word_split('Hello', ['Hello', 'hello'])
