| """ | |
| ********** | |
| Exceptions | |
| ********** | |
| Base exceptions and errors for NetworkX. | |
| """ | |
| __all__ = [ | |
| "HasACycle", | |
| "NodeNotFound", | |
| "PowerIterationFailedConvergence", | |
| "ExceededMaxIterations", | |
| "AmbiguousSolution", | |
| "NetworkXAlgorithmError", | |
| "NetworkXException", | |
| "NetworkXError", | |
| "NetworkXNoCycle", | |
| "NetworkXNoPath", | |
| "NetworkXNotImplemented", | |
| "NetworkXPointlessConcept", | |
| "NetworkXUnbounded", | |
| "NetworkXUnfeasible", | |
| ] | |
| class NetworkXException(Exception): | |
| """Base class for exceptions in NetworkX.""" | |
| class NetworkXError(NetworkXException): | |
| """Exception for a serious error in NetworkX""" | |
| class NetworkXPointlessConcept(NetworkXException): | |
| """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(NetworkXException): | |
| """Exception for unexpected termination of algorithms.""" | |
| class NetworkXUnfeasible(NetworkXAlgorithmError): | |
| """Exception raised by algorithms trying to solve a problem | |
| instance that has no feasible solution.""" | |
| class NetworkXNoPath(NetworkXUnfeasible): | |
| """Exception for algorithms that should return a path when running | |
| on graphs where such a path does not exist.""" | |
| class NetworkXNoCycle(NetworkXUnfeasible): | |
| """Exception for algorithms that should return a cycle when running | |
| on graphs where such a cycle does not exist.""" | |
| class HasACycle(NetworkXException): | |
| """Raised if a graph has a cycle when an algorithm expects that it | |
| will have no cycles. | |
| """ | |
| class NetworkXUnbounded(NetworkXAlgorithmError): | |
| """Exception raised by algorithms trying to solve a maximization | |
| or a minimization problem instance that is unbounded.""" | |
| class NetworkXNotImplemented(NetworkXException): | |
| """Exception raised by algorithms not implemented for a type of graph.""" | |
| class NodeNotFound(NetworkXException): | |
| """Exception raised if requested node is not present in the graph""" | |
| class AmbiguousSolution(NetworkXException): | |
| """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(NetworkXException): | |
| """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(ExceededMaxIterations): | |
| """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. | |
| """ | |
| def __init__(self, num_iterations, *args, **kw): | |
| msg = f"power iteration failed to converge within {num_iterations} iterations" | |
| exception_message = msg | |
| superinit = super().__init__ | |
| superinit(self, exception_message, *args, **kw) | |