def prescan(self):
        if self.to_scan:
            map(self.scan_url, self.to_scan)
        self.to_scan = None     # from now on, go ahead and process immediately
L{_EXTRAS_REQUIRE} contains options for all documented extras: C{dev},
dataset/ETHPy150Open balanced/status.balancedpayments.com/venv/lib/python2.7/site-packages/distribute-0.6.34-py2.7.egg/setuptools/package_index.py/PackageIndex.prescan--crossover with--dataset/ETHPy150Open twisted/twisted/twisted/python/test/test_dist.py/OptionalDependenciesTests.test_extrasRequireDictContainsKeys