1"""
2**********
3Exceptions
4**********
5
6Base exceptions and errors for NetworkX.
7"""
8
9__all__ = [
10    "HasACycle",
11    "NodeNotFound",
12    "PowerIterationFailedConvergence",
13    "ExceededMaxIterations",
14    "AmbiguousSolution",
15    "NetworkXAlgorithmError",
16    "NetworkXException",
17    "NetworkXError",
18    "NetworkXNoCycle",
19    "NetworkXNoPath",
20    "NetworkXNotImplemented",
21    "NetworkXPointlessConcept",
22    "NetworkXUnbounded",
23    "NetworkXUnfeasible",
24]
25
26
27class NetworkXException(Exception):
28    """Base class for exceptions in NetworkX."""
29
30
31class NetworkXError(NetworkXException):
32    """Exception for a serious error in NetworkX"""
33
34
35class NetworkXPointlessConcept(NetworkXException):
36    """Raised when a null graph is provided as input to an algorithm
37    that cannot use it.
38
39    The null graph is sometimes considered a pointless concept [1]_,
40    thus the name of the exception.
41
42    References
43    ----------
44    .. [1] Harary, F. and Read, R. "Is the Null Graph a Pointless
45       Concept?"  In Graphs and Combinatorics Conference, George
46       Washington University.  New York: Springer-Verlag, 1973.
47
48    """
49
50
51class NetworkXAlgorithmError(NetworkXException):
52    """Exception for unexpected termination of algorithms."""
53
54
55class NetworkXUnfeasible(NetworkXAlgorithmError):
56    """Exception raised by algorithms trying to solve a problem
57    instance that has no feasible solution."""
58
59
60class NetworkXNoPath(NetworkXUnfeasible):
61    """Exception for algorithms that should return a path when running
62    on graphs where such a path does not exist."""
63
64
65class NetworkXNoCycle(NetworkXUnfeasible):
66    """Exception for algorithms that should return a cycle when running
67    on graphs where such a cycle does not exist."""
68
69
70class HasACycle(NetworkXException):
71    """Raised if a graph has a cycle when an algorithm expects that it
72    will have no cycles.
73
74    """
75
76
77class NetworkXUnbounded(NetworkXAlgorithmError):
78    """Exception raised by algorithms trying to solve a maximization
79    or a minimization problem instance that is unbounded."""
80
81
82class NetworkXNotImplemented(NetworkXException):
83    """Exception raised by algorithms not implemented for a type of graph."""
84
85
86class NodeNotFound(NetworkXException):
87    """Exception raised if requested node is not present in the graph"""
88
89
90class AmbiguousSolution(NetworkXException):
91    """Raised if more than one valid solution exists for an intermediary step
92    of an algorithm.
93
94    In the face of ambiguity, refuse the temptation to guess.
95    This may occur, for example, when trying to determine the
96    bipartite node sets in a disconnected bipartite graph when
97    computing bipartite matchings.
98
99    """
100
101
102class ExceededMaxIterations(NetworkXException):
103    """Raised if a loop iterates too many times without breaking.
104
105    This may occur, for example, in an algorithm that computes
106    progressively better approximations to a value but exceeds an
107    iteration bound specified by the user.
108
109    """
110
111
112class PowerIterationFailedConvergence(ExceededMaxIterations):
113    """Raised when the power iteration method fails to converge within a
114    specified iteration limit.
115
116    `num_iterations` is the number of iterations that have been
117    completed when this exception was raised.
118
119    """
120
121    def __init__(self, num_iterations, *args, **kw):
122        msg = f"power iteration failed to converge within {num_iterations} iterations"
123        exception_message = msg
124        superinit = super().__init__
125        superinit(self, exception_message, *args, **kw)
126