Entry Point for completion of main and subcommand options.

def autocomplete():
    """Entry Point for completion of main and subcommand options.
    """
    # Don't complete if user hasn't sourced bash_completion file.
    if 'PIP_AUTO_COMPLETE' not in os.environ:
        return
    cwords = os.environ['COMP_WORDS'].split()[1:]
    cword = int(os.environ['COMP_CWORD'])
    try:
        current = cwords[cword - 1]
    except IndexError:
        current = ''

    subcommands = [cmd for cmd, summary in get_summaries()]
    options = []
    # subcommand
    try:
        subcommand_name = [w for w in cwords if w in subcommands][0]
    except IndexError:
        subcommand_name = None

    parser = create_main_parser()
    # subcommand options
    if subcommand_name:
        # special case: 'help' subcommand has no options
        if subcommand_name == 'help':
            sys.exit(1)
        # special case: list locally installed dists for show and uninstall
        should_list_installed = (
            subcommand_name in ['show', 'uninstall'] and
            not current.startswith('-')
        )
        if should_list_installed:
            installed = []
            lc = current.lower()
            for dist in get_installed_distributions(local_only=True):
                if dist.key.startswith(lc) and dist.key not in cwords[1:]:
                    installed.append(dist.key)
            # if there are no dists installed, fall back to option completion
            if installed:
                for dist in installed:
                    print(dist)
                sys.exit(1)

        subcommand = commands_dict[subcommand_name]()

        for opt in subcommand.parser.option_list_all:
            if opt.help != optparse.SUPPRESS_HELP:
                for opt_str in opt._long_opts + opt._short_opts:
                    options.append((opt_str, opt.nargs))

        # filter out previously specified options from available options
        prev_opts = [x.split('=')[0] for x in cwords[1:cword - 1]]
        options = [(x, v) for (x, v) in options if x not in prev_opts]
        # filter options by current input
        options = [(k, v) for k, v in options if k.startswith(current)]
        # get completion type given cwords and available subcommand options
        completion_type = get_path_completion_type(
            cwords, cword, subcommand.parser.option_list_all,
        )
        # get completion files and directories if ``completion_type`` is
        # ``<file>``, ``<dir>`` or ``<path>``
        if completion_type:
            options = auto_complete_paths(current, completion_type)
            options = ((opt, 0) for opt in options)
        for option in options:
            opt_label = option[0]
            # append '=' to options which require args
            if option[1] and option[0][:2] == "--":
                opt_label += '='
            print(opt_label)
    else:
        # show main parser options only when necessary

        opts = [i.option_list for i in parser.option_groups]
        opts.append(parser.option_list)
        opts = (o for it in opts for o in it)
        if current.startswith('-'):
            for opt in opts:
                if opt.help != optparse.SUPPRESS_HELP:
                    subcommands += opt._long_opts + opt._short_opts
        else:
            # get completion type given cwords and all available options
            completion_type = get_path_completion_type(cwords, cword, opts)
            if completion_type:
                subcommands = auto_complete_paths(current, completion_type)

        print(' '.join([x for x in subcommands if x.startswith(current)]))
    sys.exit(1)