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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_mirror_urls(self, mirrors=None, main_mirror_url=None):
 """Retrieves a list of URLs from the main mirror DNS entry unless a list of mirror URLs are passed. """

        if not mirrors:
            mirrors = get_mirrors(main_mirror_url)
            # Should this be made "less random"? E.g. netselect like?
            random.shuffle(mirrors)

        mirror_urls = set()
        for mirror_url in mirrors:
            # Make sure we have a valid URL
            if not ("http://" or "https://" or "file://") in mirror_url:
                mirror_url = "http://%s" % mirror_url
            if not mirror_url.endswith("/simple"):
                mirror_url = "%s/simple/" % mirror_url
            mirror_urls.add(mirror_url)

        return list(mirror_urls)