def process_line(line, filename, line_number, finder=None, comes_from=None,
                 options=None, session=None, wheel_cache=None,
                 constraint=False):
    """Process a single requirements line; This can result in creating/yielding
    requirements, or updating the finder.

    For lines that contain requirements, the only options that have an effect
    are from SUPPORTED_OPTIONS_REQ, and they are scoped to the
    requirement. Other options from SUPPORTED_OPTIONS may be present, but are
    ignored.

    For lines that do not contain requirements, the only options that have an
    effect are from SUPPORTED_OPTIONS. Options from SUPPORTED_OPTIONS_REQ may
    be present, but are ignored. These lines may contain multiple options
    (although our docs imply only one is supported), and all our parsed and
    affect the finder.

    :param constraint: If True, parsing a constraints file.
    :param options: OptionParser options that we may update
    """
    parser = build_parser()
    defaults = parser.get_default_values()
    defaults.index_url = None
    if finder:
        # `finder.format_control` will be updated during parsing
        defaults.format_control = finder.format_control
    args_str, options_str = break_args_options(line)
    if sys.version_info < (2, 7, 3):
        # Priori to 2.7.3, shlex can not deal with unicode entries
        options_str = options_str.encode('utf8')
    opts, _ = parser.parse_args(shlex.split(options_str), defaults)

    # preserve for the nested code path
    line_comes_from = '%s %s (line %s)' % (
        '-c' if constraint else '-r', filename, line_number)

    # yield a line requirement
    if args_str:
        isolated = options.isolated_mode if options else False
        if options:
            cmdoptions.check_install_build_global(options, opts)
        # get the options that apply to requirements
        req_options = {}
        for dest in SUPPORTED_OPTIONS_REQ_DEST:
            if opts.__dict__ in dest and opts.__dict__[dest]:
                req_options[dest] = opts.__dict__[dest]
        yield InstallRequirement.from_line(
            args_str, line_comes_from, constraint=constraint,
            isolated=isolated, options=req_options, wheel_cache=wheel_cache
        )

    # yield an editable requirement
    elif opts.editables:
        isolated = options.isolated_mode if options else False
        default_vcs = options.default_vcs if options else None
        yield InstallRequirement.from_editable(
            opts.editables[0], comes_from=line_comes_from,
            constraint=constraint, default_vcs=default_vcs, isolated=isolated,
            wheel_cache=wheel_cache
        )

    # parse a nested requirements file
    elif opts.requirements or opts.constraints:
        if opts.requirements:
            req_path = opts.requirements[0]
            nested_constraint = False
        else:
            req_path = opts.constraints[0]
            nested_constraint = True
        # original file is over http
        if SCHEME_RE.search(filename):
            # do a url join so relative paths work
            req_path = urllib_parse.urljoin(filename, req_path)
        # original file and nested file are paths
        elif not SCHEME_RE.search(req_path):
            # do a join so relative paths work
            req_path = os.path.join(os.path.dirname(filename), req_path)
        # TODO: Why not use `comes_from='-r {} (line {})'` here as well?
        parser = parse_requirements(
            req_path, finder, comes_from, options, session,
            constraint=nested_constraint, wheel_cache=wheel_cache
        )
        for req in parser:
            yield req

    # percolate hash-checking option upward
    elif opts.require_hashes:
        options.require_hashes = opts.require_hashes

    # set finder options
    elif finder:
        if opts.allow_external:
            warnings.warn(
                "--allow-external has been deprecated and will be removed in "
                "the future. Due to changes in the repository protocol, it no "
                "longer has any effect.",
                RemovedInPip10Warning,
            )

        if opts.allow_all_external:
            warnings.warn(
                "--allow-all-external has been deprecated and will be removed "
                "in the future. Due to changes in the repository protocol, it "
                "no longer has any effect.",
                RemovedInPip10Warning,
            )

        if opts.allow_unverified:
            warnings.warn(
                "--allow-unverified has been deprecated and will be removed "
                "in the future. Due to changes in the repository protocol, it "
                "no longer has any effect.",
                RemovedInPip10Warning,
            )

        if opts.index_url:
            finder.index_urls = [opts.index_url]
        if opts.use_wheel is False:
            finder.use_wheel = False
            pip.index.fmt_ctl_no_use_wheel(finder.format_control)
        if opts.no_index is True:
            finder.index_urls = []
        if opts.extra_index_urls:
            finder.index_urls.extend(opts.extra_index_urls)
        if opts.find_links:
            # FIXME: it would be nice to keep track of the source
            # of the find_links: support a find-links local path
            # relative to a requirements file.
            value = opts.find_links[0]
            req_dir = os.path.dirname(os.path.abspath(filename))
            relative_to_reqs_file = os.path.join(req_dir, value)
            if os.path.exists(relative_to_reqs_file):
                value = relative_to_reqs_file
            finder.find_links.append(value)
        if opts.pre:
            finder.allow_all_prereleases = True
        if opts.process_dependency_links:
            finder.process_dependency_links = True
        if opts.trusted_hosts:
            finder.secure_origins.extend(
                ("*", host, "*") for host in opts.trusted_hosts)
dataset/ETHPy150Open pypa/pip/pip/req/req_file.py/process_line/swapped operands of `in`