chore: import upstream snapshot with attribution

easygraph/exception.py

@@ -0,0 +1,84 @@
+"""
+**********
+Exceptions
+**********
+
+Base exceptions and errors for EasyGraph.
+"""
+
+__all__ = [
+    "HasACycle",
+    "NodeNotFound",
+    "EasyGraphAlgorithmError",
+    "EasyGraphException",
+    "EasyGraphError",
+    "EasyGraphNoCycle",
+    "EasyGraphNoPath",
+    "EasyGraphNotImplemented",
+    "EasyGraphPointlessConcept",
+    "EasyGraphUnbounded",
+    "EasyGraphUnfeasible",
+]
+
+
+class EasyGraphException(Exception):
+    """Base class for exceptions in EasyGraph."""
+
+
+class EasyGraphError(EasyGraphException):
+    """Exception for a serious error in EasyGraph"""
+
+
+class EasyGraphPointlessConcept(EasyGraphException):
+    """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.
+
+    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 EasyGraphAlgorithmError(EasyGraphException):
+    """Exception for unexpected termination of algorithms."""
+
+
+class EasyGraphUnfeasible(EasyGraphAlgorithmError):
+    """Exception raised by algorithms trying to solve a problem
+    instance that has no feasible solution."""
+
+
+class EasyGraphNoPath(EasyGraphUnfeasible):
+    """Exception for algorithms that should return a path when running
+    on graphs where such a path does not exist."""
+
+
+class EasyGraphNoCycle(EasyGraphUnfeasible):
+    """Exception for algorithms that should return a cycle when running
+    on graphs where such a cycle does not exist."""
+
+
+class HasACycle(EasyGraphException):
+    """Raised if a graph has a cycle when an algorithm expects that it
+    will have no cycles.
+
+    """
+
+
+class EasyGraphUnbounded(EasyGraphAlgorithmError):
+    """Exception raised by algorithms trying to solve a maximization
+    or a minimization problem instance that is unbounded."""
+
+
+class EasyGraphNotImplemented(EasyGraphException):
+    """Exception raised by algorithms not implemented for a type of graph."""
+
+
+class NodeNotFound(EasyGraphException):
+    """Exception raised if requested node is not present in the graph"""