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# (C) Copyright 2005-2023 Enthought, Inc., Austin, TX
# All rights reserved.
#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
# the conditions described in the aforementioned license. The license
# is also available online at http://www.enthought.com/licenses/BSD.txt
#
# Thanks for using Enthought open source!
""" A simple topological sort on a dictionary graph.
"""
class CyclicGraph(Exception):
"""
Exception for cyclic graphs.
"""
def __init__(self):
Exception.__init__(self, "Graph is cyclic")
def topological_sort(graph):
"""
Returns the nodes in the graph in topological order.
"""
discovered = {}
explored = {}
order = []
def explore(node):
children = graph.get(node, [])
for child in children:
if child in explored:
pass
elif child in discovered:
raise CyclicGraph()
else:
discovered[child] = 1
explore(child)
explored[node] = 1
order.append(node)
for node in graph.keys():
if node not in explored:
explore(node)
order.reverse()
return order
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