larzgraph

Graphs and the everyday algorithms. Pure Python, zero dependencies.

The useful 90% of a graph library, tiny: build a directed or undirected weighted graph and run traversal, shortest paths, connectivity, ordering, and cycle detection — no networkx, no numpy, nothing to install.

from larzgraph import Graph, DiGraph

g = Graph()
g.add_edge("a", "b"); g.add_edge("b", "c", weight=2)
g.shortest_path("a", "c")          # (['a', 'b', 'c'], 3)
g.connected_components()

dag = DiGraph()
dag.add_edges([("build", "test"), ("test", "deploy")])
dag.topological_sort()             # ['build', 'test', 'deploy']
dag.has_cycle()                    # False

Why

• The algorithms you actually use — BFS, DFS, Dijkstra shortest paths, connected components, topological sort, cycle detection, and strongly-connected components (Tarjan) — without importing a scientific stack.
• Directed and undirected, weighted, with a clean small API.
• Deterministic — traversal and topological order break ties in sorted order, so results are reproducible and testable.
• Zero dependencies. Great for build-order resolution, dependency graphs, routing, task scheduling, and teaching — anywhere networkx is overkill.

Install

pip install larzgraph

Usage

from larzgraph import Graph, DiGraph

g = Graph()                              # undirected
g.add_edges([("a", "b"), ("b", "c", 4)]) # weight optional (default 1)
g.neighbors("b"); g.degree("b"); g.weight("b", "c")

g.bfs("a"); g.dfs("a")                   # traversal order
g.has_path("a", "c")
g.shortest_path("a", "c")                # (path, distance) via Dijkstra
g.connected_components(); g.is_connected()
g.has_cycle()

d = DiGraph()                            # directed
d.add_edges([("a", "b"), ("b", "c"), ("c", "a")])
d.topological_sort()                     # raises CycleError here
d.has_cycle(); d.is_dag()
d.strongly_connected_components()        # [['a', 'b', 'c']]
d.weakly_connected_components()

Tests

python -m unittest discover -s tests -v   # 24 tests, zero deps

The Larz stack

Pure-Python, zero-dependency building blocks: larz · larzchain · larzmoney · larzcrypt · larzdb · larzagent · larzchart · larzmark · larztask · larzvault · larzvm · larzcache · larzvalidate · larzid · larzrpc · larzstate · larzhttp · larzconf · larzcron · larzlimit · larzlog · larzcli · larzretry · larztime · larzpdf · larzpack · larztemplate · larzcolor · larztable · larzjson · larzbus · larzmigrate · larzgraph

License

MIT © larz-scripter