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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 requires(self, extras=()):
 """List of Requirements needed for this distro if `extras` are used"""

        dm = self._dep_map
        deps = []
        deps.extend(dm.get(None, ()))
        for ext in extras:
            try:
                deps.extend(dm[safe_extra(ext)])
            except KeyError:
                raise UnknownExtra(
                    "%s has no such extra feature %r" % (self, ext)
                )
        return deps