def _prepare_file(self, finder, req_to_install):
        """Prepare a single requirements files.

        :return: A list of addition InstallRequirements to also install.
        """
        # Tell user what we are doing for this requirement:
        # obtain (editable), skipping, processing (local url), collecting
        # (remote url or package name)
        if req_to_install.constraint or req_to_install.prepared:
            return []

        req_to_install.prepared = True

        if req_to_install.editable:
            logger.info('Obtaining %s', req_to_install)
        else:
            # satisfied_by is only evaluated by calling _check_skip_installed,
            # so it must be None here.
            assert req_to_install.satisfied_by is None
            if not self.ignore_installed:
                skip_reason = self._check_skip_installed(
                    req_to_install, finder)

            if req_to_install.satisfied_by:
                assert skip_reason is not None, (
                    '_check_skip_installed returned None but '
                    'req_to_install.satisfied_by is set to %r'
                    % (req_to_install.satisfied_by,))
                logger.info(
                    'Requirement already %s: %s', skip_reason,
                    req_to_install)
            else:
                if (req_to_install.link and
                        req_to_install.link.scheme == 'file'):
                    path = url_to_path(req_to_install.link.url)
                    logger.info('Processing %s', display_path(path))
                else:
                    logger.info('Collecting %s', req_to_install)

        with indent_log():
            # ################################ #
            # # vcs update or unpack archive # #
            # ################################ #
            if req_to_install.editable:
                req_to_install.ensure_has_source_dir(self.src_dir)
                req_to_install.update_editable(not self.is_download)
                abstract_dist = make_abstract_dist(req_to_install)
                abstract_dist.prep_for_dist()
                if self.is_download:
                    req_to_install.archive(self.download_dir)
            elif req_to_install.satisfied_by:
                abstract_dist = Installed(req_to_install)
            else:
                # @@ if filesystem packages are not marked
                # editable in a req, a non deterministic error
                # occurs when the script attempts to unpack the
                # build directory
                req_to_install.ensure_has_source_dir(self.build_dir)
                # If a checkout exists, it's unwise to keep going.  version
                # inconsistencies are logged later, but do not fail the
                # installation.
                # FIXME: this won't upgrade when there's an existing
                # package unpacked in `req_to_install.source_dir`
                if os.path.exists(
                        os.path.join(req_to_install.source_dir, 'setup.py')):
                    raise PreviousBuildDirError(
                        "pip can't proceed with requirements '%s' due to a"
                        " pre-existing build directory (%s). This is "
                        "likely due to a previous installation that failed"
                        ". pip is being responsible and not assuming it "
                        "can delete this. Please delete it and try again."
                        % (req_to_install, req_to_install.source_dir)
                    )
                req_to_install.populate_link(finder, self.upgrade)
                # We can't hit this spot and have populate_link return None.
                # req_to_install.satisfied_by is None here (because we're
                # guarded) and upgrade has no impact except when satisfied_by
                # is not None.
                # Then inside find_requirement existing_applicable -> False
                # If no new versions are found, DistributionNotFound is raised,
                # otherwise a result is guaranteed.
                assert req_to_install.link
                try:
                    download_dir = self.download_dir
                    # We always delete unpacked sdists after pip ran.
                    autodelete_unpacked = True
                    if req_to_install.link.is_wheel \
                            and self.wheel_download_dir:
                        # when doing 'pip wheel` we download wheels to a
                        # dedicated dir.
                        download_dir = self.wheel_download_dir
                    if req_to_install.link.is_wheel:
                        if download_dir:
                            # When downloading, we only unpack wheels to get
                            # metadata.
                            autodelete_unpacked = True
                        else:
                            # When installing a wheel, we use the unpacked
                            # wheel.
                            autodelete_unpacked = False
                    unpack_url(
                        req_to_install.link, req_to_install.source_dir,
                        download_dir, autodelete_unpacked,
                        session=self.session)
                except requests.HTTPError as exc:
                    logger.critical(
                        'Could not install requirement %s because '
                        'of error %s',
                        req_to_install,
                        exc,
                    )
                    raise InstallationError(
                        'Could not install requirement %s because '
                        'of HTTP error %s for URL %s' %
                        (req_to_install, exc, req_to_install.link)
                    )
                abstract_dist = make_abstract_dist(req_to_install)
                abstract_dist.prep_for_dist()
                if self.is_download:
                    # Make a .zip of the source_dir we already created.
                    if vcs.all_schemes in req_to_install.link.scheme:
                        req_to_install.archive(self.download_dir)
                # req_to_install.req is only avail after unpack for URL
                # pkgs repeat check_if_exists to uninstall-on-upgrade
                # (#14)
                if not self.ignore_installed:
                    req_to_install.check_if_exists()
                if req_to_install.satisfied_by:
                    if self.upgrade or self.ignore_installed:
                        # don't uninstall conflict if user install and
                        # conflict is not user install
                        if not (self.use_user_site and not
                                dist_in_usersite(
                                    req_to_install.satisfied_by)):
                            req_to_install.conflicts_with = \
                                req_to_install.satisfied_by
                        req_to_install.satisfied_by = None
                    else:
                        logger.info(
                            'Requirement already satisfied (use '
                            '--upgrade to upgrade): %s',
                            req_to_install,
                        )

            # ###################### #
            # # parse dependencies # #
            # ###################### #
            dist = abstract_dist.dist(finder)
            more_reqs = []

            def add_req(subreq):
                sub_install_req = InstallRequirement(
                    str(subreq),
                    req_to_install,
                    isolated=self.isolated,
                    wheel_cache=self._wheel_cache,
                )
                more_reqs.extend(self.add_requirement(
                    sub_install_req, req_to_install.name))

            # We add req_to_install before its dependencies, so that we
            # can refer to it when adding dependencies.
            if not self.has_requirement(req_to_install.name):
                # 'unnamed' requirements will get added here
                self.add_requirement(req_to_install, None)

            if not self.ignore_dependencies:
                if (req_to_install.extras):
                    logger.debug(
                        "Installing extra requirements: %r",
                        ','.join(req_to_install.extras),
                    )
                missing_requested = sorted(
                    set(req_to_install.extras) - set(dist.extras)
                )
                for missing in missing_requested:
                    logger.warning(
                        '%s does not provide the extra \'%s\'',
                        dist, missing
                    )

                available_requested = sorted(
                    set(dist.extras) & set(req_to_install.extras)
                )
                for subreq in dist.requires(available_requested):
                    add_req(subreq)

            # cleanup tmp src
            self.reqs_to_cleanup.append(req_to_install)

            if not req_to_install.editable and not req_to_install.satisfied_by:
                # XXX: --no-install leads this to report 'Successfully
                # downloaded' for only non-editable reqs, even though we took
                # action on them.
                self.successfully_downloaded.append(req_to_install)

        return more_reqs
dataset/ETHPy150Open anzev/hedwig/build/pip/pip/req/req_set.py/RequirementSet._prepare_file/swapped operands of `in`