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Graph Helpers

This page documents all user-facing graph APIs for var when holding a graph, in a clear, tabular format with concise, non-redundant examples. Multi-step and real-world examples are at the end.

Graph API Reference

Properties & Queries

Method	Description	Example
`size_t node_count()`	Number of nodes	`g.node_count()`
`size_t edge_count()`	Number of edges	`g.edge_count()`
`bool is_connected()`	Is the graph connected?	`g.is_connected()`
`bool has_cycle()`	Does the graph have a cycle?	`g.has_cycle()`
`bool has_edge(size_t from, size_t to)`	Is there an edge from→to?	`g.has_edge(0, 1)`
`std::optional<double> get_edge_weight(size_t from, size_t to)`	Get edge weight (if any)	`g.get_edge_weight(0, 1)`
`size_t out_degree(size_t node)`	Out-degree of node	`g.out_degree(0)`
`size_t in_degree(size_t node)`	In-degree of node	`g.in_degree(0)`
`var neighbors(size_t node)`	List of neighbors for node	`g.neighbors(0)`
`var get_edges(size_t node)`	List of edges for node	`g.get_edges(0)`

Node & Edge Manipulation

Method	Description	Example
`size_t add_node()`	Add empty node, return id	`g.add_node()`
`size_t add_node(const var &data)`	Add node with data, return id	`g.add_node("foo")`
`void remove_node(size_t node)`	Remove node by id	`g.remove_node(0)`
`void add_edge(size_t u, size_t v, bool directed=false, double w1=0.0, double w2=NaN)`	Add edge (optionally directed/weighted)	`g.add_edge(0, 1, true)`
`bool remove_edge(size_t from, size_t to, bool remove_reverse=true)`	Remove edge (optionally reverse)	`g.remove_edge(0, 1)`
`void set_edge_weight(size_t from, size_t to, double weight)`	Set edge weight	`g.set_edge_weight(0, 1, 3.14)`
`void set_node_data(size_t node, const var &data)`	Set node data	`g.set_node_data(0, "foo")`
`var &get_node_data(size_t node)`	Get node data (reference)	`g.get_node_data(0)`

Algorithms

Method	Description	Example
`var dfs(size_t start=0, bool recursive=true)`	Depth-first search	`g.dfs(0)`
`var bfs(size_t start=0)`	Breadth-first search	`g.bfs(0)`
`var get_shortest_path(size_t src, size_t dest)`	Shortest path (Dijkstra)	`g.get_shortest_path(0, 2)`
`var bellman_ford(size_t src)`	Bellman-Ford shortest paths	`g.bellman_ford(0)`
`var floyd_warshall()`	Floyd-Warshall all-pairs shortest paths	`g.floyd_warshall()`
`var topological_sort()`	Topological sort (DAGs)	`g.topological_sort()`
`var connected_components()`	List of connected components	`g.connected_components()`
`var strongly_connected_components()`	List of strongly connected components	`g.strongly_connected_components()`
`var prim_mst()`	Minimum spanning tree (Prim's)	`g.prim_mst()`

File/Export & Visualization

Method	Description	Example
`void save_graph(const std::string &filename)`	Save graph to file	`g.save_graph("g.txt")`
`void to_dot(const std::string &filename, bool show_weights=true)`	Export to Graphviz DOT	`g.to_dot("g.dot")`
`void show(bool layout=true)`	Show interactive graph viewer (if enabled)	`g.show()` or `g.show(false)`

Interactive Graph Viewer

The interactive viewer lets you visualize, edit, and explore graphs in real time (requires build with -DPYTHONIC_ENABLE_GRAPH_VIEWER=ON).

Usage:

g.show();           // auto-layout
g.show(false);      // preserve node positions

Features:

View: drag nodes, hover for metadata, click for animation
Edit: double-click to add nodes, drag to add edges, select+delete to remove
All changes are saved back to your var graph

Examples

Basic Graph Creation & Manipulation

var g = graph();
auto n0 = g.add_node("A");
auto n1 = g.add_node("B");
g.add_edge(n0, n1, 1.5);
g.set_node_data(n0, "Alpha");
print(g.node_count()); // 2
print(g.edge_count()); // 1
print(g.has_edge(n0, n1)); // true
print(g.get_edge_weight(n0, n1)); // 1.5
print(g.get_node_data(n0)); // "Alpha"
print(g.dfs(n0)); // DFS traversal from node n0
g.save_graph("g.txt");
g.to_dot("g.dot");

Graph Properties & Traversals

var g = graph(5);
g.add_edge(0, 1);
g.add_edge(1, 2);
g.add_edge(2, 3);
g.add_edge(3, 4);
print(g.is_connected());  // true
print(g.has_cycle());     // false
g.add_edge(4, 0);
print(g.has_cycle());     // true
print(g.out_degree(0));   // outgoing edges from node 0
print(g.in_degree(0));    // incoming edges to node 0
print(g.neighbors(0));    // neighbors of node 0
print(g.get_edges(0));    // edges from node 0

Shortest Paths & Algorithms

var g = graph(5);
g.add_edge(0, 1, 4.0);
g.add_edge(0, 2, 1.0);
g.add_edge(1, 3, 1.0);
g.add_edge(2, 1, 2.0);
g.add_edge(2, 3, 5.0);
g.add_edge(3, 4, 3.0);
var result = g.get_shortest_path(0, 4);
print(result["path"]);      // [0, 2, 1, 3, 4]
print(result["distance"]);  // 7.0
var bf = g.bellman_ford(0);
print(bf["distances"]);     // [0, 3, 1, 4, 7]
var fw = g.floyd_warshall();
for_each(row, fw) print(row);

Components, Topological Sort, MST

var dag = graph(4);
dag.add_edge(0, 1, true, 1.0);  // directed edge
dag.add_edge(0, 2, true, 1.0);  // directed edge
dag.add_edge(1, 3, true, 1.0);  // directed edge
dag.add_edge(2, 3, true, 1.0);  // directed edge
print(dag.topological_sort());

var network = graph(6);
network.add_edge(0, 1);
network.add_edge(1, 2);
network.add_edge(3, 4);
network.add_edge(4, 5);
print(network.connected_components());

var city_network = graph(4);
city_network.add_edge(0, 1, 1.0);
city_network.add_edge(0, 2, 4.0);
city_network.add_edge(1, 2, 2.0);
city_network.add_edge(1, 3, 5.0);
city_network.add_edge(2, 3, 3.0);
var mst = city_network.prim_mst();
print(mst["weight"]);  // 6.0
print(mst["edges"]);   // MST edge list

Serialization & Loading

var g = graph(3);
g.add_edge(0, 1, 1.5);
g.add_edge(1, 2, 2.5);
g.set_node_data(0, "Start");
g.save_graph("my_graph.txt");
var loaded = load_graph("my_graph.txt");
print(loaded.str());
g.to_dot("my_graph.dot");

Performance Optimization

var g = graph(1000);
g.reserve_edges_per_node(10);
for (size_t i = 0; i < 1000; i++)
	for (int j = 0; j < 10; j++)
		g.add_edge(i, (i + j + 1) % 1000, 1.0);
var counts = list(5, 10, 3, 8, 2);
var custom = graph(5);
custom.reserve_edges_by_counts(counts);

Notes

All graph helpers are only available when var holds a graph.
Most methods return var or standard types; see API for details.
For advanced graph algorithms, see the full API or source.
show(layout) — If layout is true (default), the viewer will automatically arrange the graph layout. If false, the current node positions are preserved.

Example for you:

// Test file for all graph_helpers.md documentation examples
#include <pythonic/pythonic.hpp>
#include <iostream>
using namespace py;

int main()
{
    // Basic Graph Creation & Manipulation
    {
        var g = graph(0);
        auto n0 = g.add_node("A");
        auto n1 = g.add_node("B");
        g.add_edge(n0, n1, 1.5);
        g.set_node_data(n0, "Alpha");
        std::cout << g.node_count() << std::endl;
        std::cout << g.edge_count() << std::endl;
        std::cout << g.has_edge(n0, n1) << std::endl;
        std::cout << g.get_edge_weight(n0, n1).value_or(-1) << std::endl;
        std::cout << g.get_node_data(n0) << std::endl;
        std::cout << g.dfs(n0) << std::endl;
        g.save_graph("/tmp/g.txt");
        g.to_dot("/tmp/g.dot");
    }
    // Graph Properties & Traversals
    {
        var g = graph(5);
        g.add_edge(0, 1);
        g.add_edge(1, 2);
        g.add_edge(2, 3);
        g.add_edge(3, 4);
        std::cout << g.is_connected() << std::endl;
        std::cout << g.has_cycle() << std::endl;
        g.add_edge(4, 0);
        std::cout << g.has_cycle() << std::endl;
        std::cout << g.out_degree(0) << std::endl;
        std::cout << g.in_degree(0) << std::endl;
        std::cout << g.neighbors(0) << std::endl;
        std::cout << g.get_edges(0) << std::endl;
    }
    // Shortest Paths & Algorithms
    {
        var g = graph(5);
        g.add_edge(0, 1, 4.0);
        g.add_edge(0, 2, 1.0);
        g.add_edge(1, 3, 1.0);
        g.add_edge(2, 1, 2.0);
        g.add_edge(2, 3, 5.0);
        g.add_edge(3, 4, 3.0);
        var result = g.get_shortest_path(0, 4);
        std::cout << result["path"] << std::endl;
        std::cout << result["distance"] << std::endl;
        var bf = g.bellman_ford(0);
        std::cout << bf["distances"] << std::endl;
        var fw = g.floyd_warshall();
        for (const auto &row : fw)
            std::cout << row << std::endl;
    }
    // Components, Topological Sort, MST
    {
        var dag = graph(4);
        dag.add_edge(0, 1, 1.0, 0.0, true);
        dag.add_edge(0, 2, 1.0, 0.0, true);
        dag.add_edge(1, 3, 1.0, 0.0, true);
        dag.add_edge(2, 3, 1.0, 0.0, true);
        std::cout << dag.topological_sort() << std::endl;
        var network = graph(6);
        network.add_edge(0, 1);
        network.add_edge(1, 2);
        network.add_edge(3, 4);
        network.add_edge(4, 5);
        std::cout << network.connected_components() << std::endl;
        var city_network = graph(4);
        city_network.add_edge(0, 1, 1.0);
        city_network.add_edge(0, 2, 4.0);
        city_network.add_edge(1, 2, 2.0);
        city_network.add_edge(1, 3, 5.0);
        city_network.add_edge(2, 3, 3.0);
        var mst = city_network.prim_mst();
        std::cout << mst["weight"] << std::endl;
        std::cout << mst["edges"] << std::endl;
    }
    // Serialization & Loading
    {
        var g = graph(3);
        g.add_edge(0, 1, 1.5);
        g.add_edge(1, 2, 2.5);
        g.set_node_data(0, "Start");
        g.save_graph("/tmp/my_graph.txt");
        var loaded = load_graph("/tmp/my_graph.txt");
        std::cout << loaded.str() << std::endl;
        g.to_dot("/tmp/my_graph.dot");
    }
    // Performance Optimization
    {
        var g = graph(1000);
        g.reserve_edges_per_node(10);
        for (size_t i = 0; i < 1000; i++)
            for (int j = 0; j < 10; j++)
                g.add_edge(i, (i + j + 1) % 1000, 1.0);
        var counts = list(5, 10, 3, 8, 2);
        var custom = graph(5);
        custom.reserve_edges_by_counts(counts);
    }
    return 0;
}

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Graph Helpers

Graph API Reference

Properties & Queries

Node & Edge Manipulation

Algorithms

File/Export & Visualization

Interactive Graph Viewer

Examples

Basic Graph Creation & Manipulation

Graph Properties & Traversals

Shortest Paths & Algorithms

Components, Topological Sort, MST

Serialization & Loading

Performance Optimization

Notes

Example for you:

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Graph Helpers

Graph API Reference

Properties & Queries

Node & Edge Manipulation

Algorithms

File/Export & Visualization

Interactive Graph Viewer

Examples

Basic Graph Creation & Manipulation

Graph Properties & Traversals

Shortest Paths & Algorithms

Components, Topological Sort, MST

Serialization & Loading

Performance Optimization

Notes

Example for you:

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