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# Source code for networkx.readwrite.adjlist

    """
    **************
    Adjacency List
    **************
    Read and write NetworkX graphs as adjacency lists.

    Adjacency list format is useful for graphs without data associated
    with nodes or edges and for nodes that can be meaningfully represented
    as strings.

    Format
    ------
    The adjacency list format consists of lines with node labels.  The
    first label in a line is the source node.  Further labels in the line
    are considered target nodes and are added to the graph along with an edge
    between the source node and target node.

    The graph with edges a-b, a-c, d-e can be represented as the following
    adjacency list (anything following the # in a line is a comment)::

         a b c # source target target
         d e
    """

    __all__ = ["generate_adjlist", "write_adjlist", "parse_adjlist", "read_adjlist"]

    import networkx as nx
    from networkx.utils import open_file

    def generate_adjlist(G, delimiter=" "):
        """Generate a single line of the graph G in adjacency list format.

        Parameters
        ----------
        G : NetworkX graph

        delimiter : string, optional
           Separator for node labels

        Returns
        -------
        lines : string
            Lines of data in adjlist format.

        Examples
        --------
        >>> G = nx.lollipop_graph(4, 3)
        >>> for line in nx.generate_adjlist(G):
        ...     print(line)
        0 1 2 3
        1 2 3
        2 3
        3 4
        4 5
        5 6
        6

        See Also
        --------
        write_adjlist, read_adjlist

        Notes
        -----
        The default `delimiter=" "` will result in unexpected results if node names contain
        whitespace characters. To avoid this problem, specify an alternate delimiter when spaces are
        valid in node names.

        NB: This option is not available for data that isn't user-generated.

        """
        directed = G.is_directed()
        seen = set()
        for s, nbrs in G.adjacency():
            line = str(s) + delimiter
            for t, data in nbrs.items():
                if not directed and t in seen:
                    continue
                if G.is_multigraph():
                    for d in data.values():
                        line += str(t) + delimiter
                else:
                    line += str(t) + delimiter
            if not directed:
                seen.add(s)
            yield line[: -len(delimiter)]

    @open_file(1, mode="wb")
    def write_adjlist(G, path, comments="#", delimiter=" ", encoding="utf-8"):
        """Write graph G in single-line adjacency-list format to path.

        Parameters
        ----------
        G : NetworkX graph

        path : string or file
           Filename or file handle for data output.
           Filenames ending in .gz or .bz2 will be compressed.

        comments : string, optional
           Marker for comment lines

        delimiter : string, optional
           Separator for node labels

        encoding : string, optional
           Text encoding.

        Examples
        --------
        >>> G = nx.path_graph(4)
        >>> nx.write_adjlist(G, "test.adjlist")

        The path can be a filehandle or a string with the name of the file. If a
        filehandle is provided, it has to be opened in 'wb' mode.

        >>> fh = open("test.adjlist", "wb")
        >>> nx.write_adjlist(G, fh)

        Notes
        -----
        The default `delimiter=" "` will result in unexpected results if node names contain
        whitespace characters. To avoid this problem, specify an alternate delimiter when spaces are
        valid in node names.
        NB: This option is not available for data that isn't user-generated.

        This format does not store graph, node, or edge data.

        See Also
        --------
        read_adjlist, generate_adjlist
        """
        import sys
        import time

        pargs = comments + " ".join(sys.argv) + "\n"
        header = (
            pargs
            + comments
            + f" GMT {time.asctime(time.gmtime())}\n"
            + comments
            + f" {G.name}\n"
        )
        path.write(header.encode(encoding))

        for line in generate_adjlist(G, delimiter):
            line += "\n"
            path.write(line.encode(encoding))

    @nx._dispatchable(graphs=None, returns_graph=True)
    def parse_adjlist(
        lines, comments="#", delimiter=None, create_using=None, nodetype=None
    ):
        """Parse lines of a graph adjacency list representation.

        Parameters
        ----------
        lines : list or iterator of strings
            Input data in adjlist format

        create_using : NetworkX graph constructor, optional (default=nx.Graph)
           Graph type to create. If graph instance, then cleared before populated.

        nodetype : Python type, optional
           Convert nodes to this type.

        comments : string, optional
           Marker for comment lines

        delimiter : string, optional
           Separator for node labels.  The default is whitespace.

        Returns
        -------
        G: NetworkX graph
            The graph corresponding to the lines in adjacency list format.

        Examples
        --------
        >>> lines = ["1 2 5", "2 3 4", "3 5", "4", "5"]
        >>> G = nx.parse_adjlist(lines, nodetype=int)
        >>> nodes = [1, 2, 3, 4, 5]
        >>> all(node in G for node in nodes)
        True
        >>> edges = [(1, 2), (1, 5), (2, 3), (2, 4), (3, 5)]
        >>> all((u, v) in G.edges() or (v, u) in G.edges() for (u, v) in edges)
        True

        See Also
        --------
        read_adjlist

        """
        G = nx.empty_graph(0, create_using)
        for line in lines:
            p = line.find(comments)
            if p >= 0:
                line = line[:p]
            if not len(line):
                continue
            vlist = line.rstrip("\n").split(delimiter)
            u = vlist.pop(0)
            # convert types
            if nodetype is not None:
                try:
                    u = nodetype(u)
                except BaseException as err:
                    raise TypeError(
                        f"Failed to convert node ({u}) to type {nodetype}"
                    ) from err
            G.add_node(u)
            if nodetype is not None:
                try:
                    vlist = list(map(nodetype, vlist))
                except BaseException as err:
                    raise TypeError(
                        f"Failed to convert nodes ({','.join(vlist)}) to type {nodetype}"
                    ) from err
            G.add_edges_from([(u, v) for v in vlist])
        return G

    @open_file(0, mode="rb")
    @nx._dispatchable(graphs=None, returns_graph=True)
    def read_adjlist(
        path,
        comments="#",
        delimiter=None,
        create_using=None,
        nodetype=None,
        encoding="utf-8",
    ):
        """Read graph in adjacency list format from path.

        Parameters
        ----------
        path : string or file
           Filename or file handle to read.
           Filenames ending in .gz or .bz2 will be uncompressed.

        create_using : NetworkX graph constructor, optional (default=nx.Graph)
           Graph type to create. If graph instance, then cleared before populated.

        nodetype : Python type, optional
           Convert nodes to this type.

        comments : string, optional
           Marker for comment lines

        delimiter : string, optional
           Separator for node labels.  The default is whitespace.

        Returns
        -------
        G: NetworkX graph
            The graph corresponding to the lines in adjacency list format.

        Examples
        --------
        >>> G = nx.path_graph(4)
        >>> nx.write_adjlist(G, "test.adjlist")
        >>> G = nx.read_adjlist("test.adjlist")

        The path can be a filehandle or a string with the name of the file. If a
        filehandle is provided, it has to be opened in 'rb' mode.

        >>> fh = open("test.adjlist", "rb")
        >>> G = nx.read_adjlist(fh)

        Filenames ending in .gz or .bz2 will be compressed.

        >>> nx.write_adjlist(G, "test.adjlist.gz")
        >>> G = nx.read_adjlist("test.adjlist.gz")

        The optional nodetype is a function to convert node strings to nodetype.

        For example

        >>> G = nx.read_adjlist("test.adjlist", nodetype=int)

        will attempt to convert all nodes to integer type.

        Since nodes must be hashable, the function nodetype must return hashable
        types (e.g. int, float, str, frozenset - or tuples of those, etc.)

        The optional create_using parameter indicates the type of NetworkX graph
        created.  The default is `nx.Graph`, an undirected graph.
        To read the data as a directed graph use

        >>> G = nx.read_adjlist("test.adjlist", create_using=nx.DiGraph)

        Notes
        -----
        This format does not store graph or node data.

        See Also
        --------
        write_adjlist
        """
        lines = (line.decode(encoding) for line in path)
        return parse_adjlist(
            lines,
            comments=comments,
            delimiter=delimiter,
            create_using=create_using,
            nodetype=nodetype,
        )