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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 use_theme(theme, directory=None):
 """Switches to the specified theme. This returns False if switching to the already active theme."""

    repo = require_repo(directory)
    if theme not in list_themes(directory):
        raise ThemeNotFoundError(theme)

    old_theme = set_value(repo, 'theme', theme)
    return old_theme != theme