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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _build_word(syl, vowels):
 """Builds a Pinyin word re pattern from a Pinyin syllable re pattern. A word is defined as a series of consecutive valid Pinyin syllables with optional hyphens and apostrophes interspersed. Hyphens must be followed immediately by another valid Pinyin syllable. Apostrophes must be followed by another valid Pinyin syllable that starts with an 'a', 'e', or 'o'. """

    return "(?:{syl}(?:-(?={syl})|'(?=[{a}{e}{o}])(?={syl}))?)+".format(
        syl=syl, a=vowels['a'], e=vowels['e'], o=vowels['o'])