126 lines
3.5 KiB
Python
126 lines
3.5 KiB
Python
"""
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**********
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Exceptions
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**********
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Base exceptions and errors for NetworkX.
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"""
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__all__ = [
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"HasACycle",
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"NodeNotFound",
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"PowerIterationFailedConvergence",
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"ExceededMaxIterations",
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"AmbiguousSolution",
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"NetworkXAlgorithmError",
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"NetworkXException",
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"NetworkXError",
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"NetworkXNoCycle",
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"NetworkXNoPath",
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"NetworkXNotImplemented",
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"NetworkXPointlessConcept",
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"NetworkXUnbounded",
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"NetworkXUnfeasible",
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]
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class NetworkXException(Exception):
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"""Base class for exceptions in NetworkX."""
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class NetworkXError(NetworkXException):
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"""Exception for a serious error in NetworkX"""
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class NetworkXPointlessConcept(NetworkXException):
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"""Raised when a null graph is provided as input to an algorithm
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that cannot use it.
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The null graph is sometimes considered a pointless concept [1]_,
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thus the name of the exception.
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References
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----------
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.. [1] Harary, F. and Read, R. "Is the Null Graph a Pointless
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Concept?" In Graphs and Combinatorics Conference, George
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Washington University. New York: Springer-Verlag, 1973.
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"""
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class NetworkXAlgorithmError(NetworkXException):
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"""Exception for unexpected termination of algorithms."""
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class NetworkXUnfeasible(NetworkXAlgorithmError):
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"""Exception raised by algorithms trying to solve a problem
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instance that has no feasible solution."""
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class NetworkXNoPath(NetworkXUnfeasible):
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"""Exception for algorithms that should return a path when running
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on graphs where such a path does not exist."""
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class NetworkXNoCycle(NetworkXUnfeasible):
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"""Exception for algorithms that should return a cycle when running
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on graphs where such a cycle does not exist."""
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class HasACycle(NetworkXException):
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"""Raised if a graph has a cycle when an algorithm expects that it
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will have no cycles.
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"""
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class NetworkXUnbounded(NetworkXAlgorithmError):
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"""Exception raised by algorithms trying to solve a maximization
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or a minimization problem instance that is unbounded."""
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class NetworkXNotImplemented(NetworkXException):
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"""Exception raised by algorithms not implemented for a type of graph."""
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class NodeNotFound(NetworkXException):
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"""Exception raised if requested node is not present in the graph"""
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class AmbiguousSolution(NetworkXException):
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"""Raised if more than one valid solution exists for an intermediary step
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of an algorithm.
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In the face of ambiguity, refuse the temptation to guess.
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This may occur, for example, when trying to determine the
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bipartite node sets in a disconnected bipartite graph when
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computing bipartite matchings.
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"""
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class ExceededMaxIterations(NetworkXException):
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"""Raised if a loop iterates too many times without breaking.
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This may occur, for example, in an algorithm that computes
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progressively better approximations to a value but exceeds an
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iteration bound specified by the user.
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"""
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class PowerIterationFailedConvergence(ExceededMaxIterations):
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"""Raised when the power iteration method fails to converge within a
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specified iteration limit.
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`num_iterations` is the number of iterations that have been
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completed when this exception was raised.
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"""
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def __init__(self, num_iterations, *args, **kw):
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msg = f"power iteration failed to converge within {num_iterations} iterations"
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exception_message = msg
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superinit = super().__init__
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superinit(self, exception_message, *args, **kw)
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