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.

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

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

pytools.graph.compute_topological_order(graph, key=None)[source]¶

Compute a topological 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 its successor nodes.
key – A custom key function may be supplied to determine the order in break-even cases. Expects a function of one argument that is used to extract a comparison key from each node of the graph.

Returns

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

Note

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.

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