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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 short_title(self, key, value):
 """Populate the ``short_title`` key. Also populates the ``title_variants`` key through side effects. """

    short_title = value.get('a')
    title_variants = self.get('title_variants', [])

    if value.get('u'):
        short_title = value.get('u')
        title_variants.append(value.get('a'))

    self['title_variants'] = title_variants
    return short_title