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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation; either version 2 of the License, or
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# (at your option) any later version.
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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# You should have received a copy of the GNU General Public License
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# along with this program; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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from bzrlib.errors import GraphCycleError
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"""Topological sort a graph.
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graph -- sequence of pairs of node->parents_list.
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The result is a list of node names, such that all parents come before
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Nodes at the same depth are returned in sorted order.
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node identifiers can be any hashable object, and are typically strings.
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parents = {} # node -> list of parents
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children = {} # node -> list of children
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for node, node_parents in graph:
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assert node not in parents, \
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('node %r repeated in graph' % node)
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parents[node] = set(node_parents)
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if node not in children:
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children[node] = set()
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for parent in node_parents:
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if parent in children:
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children[parent].add(node)
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children[parent] = set([node])
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# find nodes with no parents, and take them now
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no_parents = [n for n in parents if len(parents[n]) == 0]
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raise GraphCycleError(parents)
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for child in children[n]:
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assert n in parents[child]
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parents[child].remove(n)
added
removed
bzrlib/tsort.py
