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Improve error message when the graph contains cyclic dependencies #33

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Improve error message when the graph contains cyclic dependencies #33

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7e34a0f
Improve error message when the graph contains cyclic dependencies
JeremyIV Jun 10, 2021
6e0cdc2
Change cyclic dependency error to a NetworkXUnfeasible error.
JeremyIV Jun 15, 2021
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19 changes: 17 additions & 2 deletions graphkit/network.py
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,14 @@ class DeleteInstruction(str):
def __repr__(self):
return 'DeleteInstruction("%s")' % self

def _format_cycle(cycle):
operation_strings = []
for second, first in reversed(cycle[1:] + [cycle[0]]):
if isinstance(first, DataPlaceholderNode) and operation_strings:
operation_strings[-1] += f' needs "{first}" from {second.name}.'
if isinstance(first, Operation):
operation_strings.append(first.name)
return "\n".join(operation_strings)

class Network(object):
"""
Expand Down Expand Up @@ -107,8 +115,15 @@ def compile(self):
self.steps = []

# create an execution order such that each layer's needs are provided.
ordered_nodes = list(nx.dag.topological_sort(self.graph))

try:
ordered_nodes = list(nx.dag.topological_sort(self.graph))
except nx.exception.NetworkXUnfeasible as ex:
try:
cycle = nx.find_cycle(self.graph)
except nx.exception.NetworkXNoCycle:
raise ex
message = f"Cyclic dependency in graph:\n{_format_cycle(cycle)}"
raise nx.exception.NetworkXUnfeasible(message)
# add Operations evaluation steps, and instructions to free data.
for i, node in enumerate(ordered_nodes):

Expand Down