python-pygraph 1.8.0-2 / usr / share / pyshared / pygraph / classes / exceptions.py

# Copyright (c) 2008-2009 Pedro Matiello <pmatiello@gmail.com>
#                         Salim Fadhley <sal@stodge.org>
#
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"""
Exceptions.
"""

# Graph errors

class GraphError(RuntimeError):
    """
    A base-class for the various kinds of errors that occur in the the python-graph class.
    """
    pass

class AdditionError(GraphError):
    """
    This error is raised when trying to add a node or edge already added to the graph or digraph.
    """
    pass

class NodeUnreachable(GraphError):
    """
    Goal could not be reached from start.
    """
    def __init__(self, start, goal):
        msg = "Node %s could not be reached from node %s" % ( repr(goal), repr(start) )
        InvalidGraphType.__init__(self, msg)
        self.start = start
        self.goal = goal

class InvalidGraphType(GraphError):
    """
    Invalid graph type.
    """
    pass

# Algorithm errors

class AlgorithmError(RuntimeError):
    """
    A base-class for the various kinds of errors that occur in the the 
    algorithms package.
    """
    pass

class NegativeWeightCycleError(AlgorithmError):
    """
    Algorithms like the Bellman-Ford algorithm can detect and raise an exception 
    when they encounter a negative weight cycle.
    
    @see: pygraph.algorithms.shortest_path_bellman_ford
    """
    pass