--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/env/lib/python3.9/site-packages/networkx/exception.py	Mon Mar 22 18:12:50 2021 +0000
@@ -0,0 +1,125 @@
+"""
+**********
+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.
+
+    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)