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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 locate(self, requirement, prereleases=False):
 """ Find the most recent distribution which matches the given requirement. :param requirement: A requirement of the form 'foo (1.0)' or perhaps 'foo (>= 1.0, < 2.0, != 1.3)' :param prereleases: If ``True``, allow pre-release versions to be located. Otherwise, pre-release versions are not returned. :return: A :class:`Distribution` instance, or ``None`` if no such distribution could be located. """

        result = None
        r = parse_requirement(requirement)
        if r is None:
            raise DistlibException('Not a valid requirement: %r' % requirement)
        scheme = get_scheme(self.scheme)
        self.matcher = matcher = scheme.matcher(r.requirement)
        logger.debug('matcher: %s (%s)', matcher, type(matcher).__name__)
        versions = self.get_project(r.name)
        if len(versions) > 2:   # urls and digests keys are present
            # sometimes, versions are invalid
            slist = []
            vcls = matcher.version_class
            for k in versions:
                if k in ('urls', 'digests'):
                    continue
                try:
                    if not matcher.match(k):
                        logger.debug('%s did not match %r', matcher, k)
                    else:
                        if prereleases or not vcls(k).is_prerelease:
                            slist.append(k)
                        else:
                            logger.debug('skipping pre-release '
                                         'version %s of %s', k, matcher.name)
                except Exception:  # pragma: no cover
                    logger.warning('error matching %s with %r', matcher, k)
                    pass # slist.append(k)
            if len(slist) > 1:
                slist = sorted(slist, key=scheme.key)
            if slist:
                logger.debug('sorted list: %s', slist)
                version = slist[-1]
                result = versions[version]
        if result:
            if r.extras:
                result.extras = r.extras
            result.download_urls = versions.get('urls', {}).get(version, set())
            d = {}
            sd = versions.get('digests', {})
            for url in result.download_urls:
                if url in sd:
                    d[url] = sd[url]
            result.digests = d
        self.matcher = None
        return result