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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 theme_get():
 """ Return the default theme The default theme is the one set (using :func:`theme_set`) by the user. If none has been set, then :class:`theme_gray` is the default. """

    from .theme_gray import theme_gray
    _theme = get_option('current_theme')
    if isinstance(_theme, type):
        _theme = _theme()
    return _theme or theme_gray()