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# Exceptions

Base exceptions and errors for NetworkX.

class NetworkXException

  Base class for exceptions in NetworkX.

class NetworkXError

  Exception for a serious error in NetworkX

class NetworkXPointlessConcept

  Raised when a null graph is provided as input to an algorithm that cannot use it.

  The null graph is sometimes considered a pointless concept [1], thus the name of the exception.

  Notes

  Null graphs and empty graphs are often used interchangeably but they are well defined in NetworkX. An `empty_graph` is a graph with `n` nodes and 0 edges, and a `null_graph` is a graph with 0 nodes and 0 edges.

  References

  [1]

  Harary, F. and Read, R. “Is the Null Graph a Pointless Concept?” In Graphs and Combinatorics Conference, George Washington University. New York: Springer-Verlag, 1973.

class NetworkXAlgorithmError

  Exception for unexpected termination of algorithms.

class NetworkXUnfeasible

  Exception raised by algorithms trying to solve a problem instance that has no feasible solution.

class NetworkXNoPath

  Exception for algorithms that should return a path when running on graphs where such a path does not exist.

class NetworkXNoCycle

  Exception for algorithms that should return a cycle when running on graphs where such a cycle does not exist.

class NodeNotFound

  Exception raised if requested node is not present in the graph

class HasACycle

  Raised if a graph has a cycle when an algorithm expects that it will have no cycles.

class NetworkXUnbounded

  Exception raised by algorithms trying to solve a maximization or a minimization problem instance that is unbounded.

class NetworkXNotImplemented

  Exception raised by algorithms not implemented for a type of graph.

class AmbiguousSolution

  Raised if more than one valid solution exists for an intermediary step of an algorithm.

  In the face of ambiguity, refuse the temptation to guess. This may occur, for example, when trying to determine the bipartite node sets in a disconnected bipartite graph when computing bipartite matchings.

class ExceededMaxIterations

  Raised if a loop iterates too many times without breaking.

  This may occur, for example, in an algorithm that computes progressively better approximations to a value but exceeds an iteration bound specified by the user.

class PowerIterationFailedConvergence(num_iterations, *args, **kw)

  Raised when the power iteration method fails to converge within a specified iteration limit.

  `num_iterations` is the number of iterations that have been completed when this exception was raised.