How to use the pipdeptree.build_dist_index function in pipdeptree

def venv_fixture(pickle_file):
    """Loads required virtualenv pkg data from a pickle file

    :param pickle_file: path to a .pickle file
    :returns: a tuple of pkgs, pkg_index, req_map
    :rtype: tuple

    """
    with open(pickle_file, 'rb') as f:
        pkgs = pickle.load(f)
        dist_index = build_dist_index(pkgs)
        tree = construct_tree(dist_index)
        return pkgs, dist_index, tree

ignore_list = [i.lower() for i in ignore_list] if ignore_list else []
    include_only = [i.lower() for i in include_only] if include_only else []
    packages = [
        package for package in
        pip.get_installed_distributions()
        if package.key not in ignore_list
    ]

    # if include_only is set, remove other packages
    if include_only:
        packages = [
            package for package in packages
            if package.key in include_only
        ]

    dist_index = pipdeptree.build_dist_index(pkgs=packages)
    tree = pipdeptree.construct_tree(index=dist_index)
    return tree

Args:
        package_name: The name of the package for which to build a dependency tree.
        local_only: Look in local distribution? Default: True.

    Returns:
        A Python list containing information about the dependencies for that package.
    """
    ## Dealing with pip 10.* api chagnes
    ## The solution is from:
    ## https://github.com/naiquevin/pipdeptree/blob/master/pipdeptree.py
    try:
        from pip._internal.utils.misc import get_installed_distributions
    except ImportError:
        from pip import get_installed_distributions
    packages = get_installed_distributions(local_only=local_only)
    dist_index = build_dist_index(packages)
    tree = sorted_tree(construct_tree(dist_index))
    nodes = tree.keys()
    # filter by our desired package only
    nodes = [p for p in nodes if p.key == package_name or p.project_name == package_name]
    if len(nodes) == 0:
        raise PackageNotFoundError(package_name)
    if len(nodes) > 1:
        raise MultiplePackagesFoundError(package_name)

    key_tree = dict((k.key, v) for k, v in iteritems(tree))
    deps = recursive_extract_dep_list(key_tree, package_name)

    unique_deps = []
    seen_deps = set()
    for dep in deps:
        if dep.key not in seen_deps: