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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 get_scraperclasses():
 """Find all comic scraper classes in the plugins directory. The result is cached. @return: list of Scraper classes @rtype: list of Scraper """

    global _scraperclasses
    if _scraperclasses is None:
        out.debug(u"Loading comic modules...")
        modules = loader.get_modules('plugins')
        plugins = loader.get_plugins(modules, Scraper)
        _scraperclasses = list(plugins)
        check_scrapers()
        out.debug(u"... %d modules loaded." % len(_scraperclasses))
    return _scraperclasses