def __init__(self, scheme='<STR_LIT:default>'):
self._cache = {}<EOL>self.scheme = scheme<EOL>self.opener = build_opener(RedirectHandler())<EOL>self.matcher = None<EOL>
Initialise an instance.
:param scheme: Because locators look for most recent versions, they
               need to know the version scheme to use. This specifies
               the current PEP-recommended scheme - use ``'legacy'``
               if you need to support existing distributions on PyPI.