Graph Algorithms

pytools.graph.a_star(initial_state, goal_state, neighbor_map, estimate_remaining_cost=None, get_step_cost=<function <lambda>>)[source]

With the default cost and heuristic, this amounts to Dijkstra’s algorithm.

pytools.graph.compute_sccs(graph)[source]
class pytools.graph.CycleError(node)[source]

Raised when a topological ordering cannot be computed due to a cycle.

Attr node

Node in a directed graph that is part of a cycle.

pytools.graph.compute_topological_order(graph)[source]

Compute a toplogical order of nodes in a directed graph.

Parameters

graph – A collections.abc.Mapping representing a directed graph. The dictionary contains one key representing each node in the graph, and this key maps to a collections.abc.Iterable of nodes that are connected to the node by outgoing edges.

Returns

A list representing a valid topological ordering of the nodes in the directed graph.

New in version 2020.2.

pytools.graph.compute_transitive_closure(graph)[source]
Compute the transitive closure of a directed graph using Warshall’s

algorithm.

Parameters

graph – A collections.abc.Mapping representing a directed graph. The dictionary contains one key representing each node in the graph, and this key maps to a collections.abc.MutableSet of nodes that are connected to the node by outgoing edges. This graph may contain cycles. This object must be picklable. Every graph node must be included as a key in the graph.

Returns

The transitive closure of the graph, represented using the same data type.

New in version 2020.2.

pytools.graph.contains_cycle(graph)[source]

Determine whether a graph contains a cycle.

Parameters

graph – A collections.abc.Mapping representing a directed graph. The dictionary contains one key representing each node in the graph, and this key maps to a collections.abc.Iterable of nodes that are connected to the node by outgoing edges.

Returns

A bool indicating whether the graph contains a cycle.

New in version 2020.2.

pytools.graph.compute_induced_subgraph(graph, subgraph_nodes)[source]
Compute the induced subgraph formed by a subset of the vertices in a

graph.

Parameters
  • graph – A collections.abc.Mapping representing a directed graph. The dictionary contains one key representing each node in the graph, and this key maps to a collections.abc.Set of nodes that are connected to the node by outgoing edges.

  • subgraph_nodes – A collections.abc.Set containing a subset of the graph nodes in the graph.

Returns

A dict representing the induced subgraph formed by the subset of the vertices included in subgraph_nodes.

New in version 2020.2.