pungi/pungi/graph.py
Ondrej Nosek cb3d36be5d Variant as a lookaside - configuration
Relates: COMPOSE-2425

Signed-off-by: Ondrej Nosek <onosek@redhat.com>
2018-04-13 14:14:43 +02:00

101 lines
3.6 KiB
Python
Executable File

# -*- coding: utf-8 -*-
class SimpleAcyclicOrientedGraph(object):
"""
Stores a graph data structure and allows operation with it.
Example data: {'P1': ['P2'], 'P3': ['P4', 'P5'], 'P2': 'P3'}
Graph is constructed by adding oriented edges one by one. It can not contain cycles.
Main result is spanning line, it determines ordering of the nodes.
"""
def __init__(self):
self._graph = {}
self._all_nodes = set()
def add_edge(self, start, end):
"""
Add one edge from node 'start' to node 'end'.
This operation must not create a cycle in the graph.
"""
if start == end:
raise ValueError("Can not add this kind of edge into graph: %s-%s" % (start, end))
self._graph.setdefault(start, [])
if end not in self._graph[start]:
self._graph[start].append(end)
self._all_nodes.add(start)
self._all_nodes.add(end)
# try to find opposite direction path (from end to start) to detect newly created cycle
path = SimpleAcyclicOrientedGraph.find_path(self._graph, end, start)
if path:
raise ValueError("There is a cycle in the graph: %s" % path)
def get_active_nodes(self):
"""
nodes connected to any edge
"""
active_nodes = set()
for start, ends in self._graph.items():
active_nodes.add(start)
active_nodes.update(ends)
return active_nodes
def is_final_endpoint(self, node):
"""
edge(s) ends in this node; no other edge starts in this node
"""
if node not in self._all_nodes:
return ValueError("This node is not found in the graph: %s" % node)
if node not in self.get_active_nodes():
return False
return False if node in self._graph else True
def remove_final_endpoint(self, node):
"""
"""
remove_start_points = []
for start, ends in self._graph.items():
if node in ends:
ends.remove(node)
if not ends:
remove_start_points.append(start)
for start in remove_start_points:
del self._graph[start]
@staticmethod
def find_path(graph, start, end, path=[]):
"""
find path among nodes 'start' and 'end' recursively
"""
path = path + [start]
if start == end:
return path
if start not in graph:
return None
for node in graph[start]:
if node not in path:
newpath = SimpleAcyclicOrientedGraph.find_path(graph, node, end, path)
if newpath:
return newpath
return None
def prune_graph(self):
"""
Construct spanning_line by pruning the graph.
Looking for endpoints and remove them one by one until graph is empty.
"""
spanning_line = []
while self._graph:
for node in sorted(self._all_nodes):
if self.is_final_endpoint(node):
self.remove_final_endpoint(node)
spanning_line.insert(0, node)
# orphan node = no edge is connected with this node
orphans = self._all_nodes - self.get_active_nodes()
if orphans:
break # restart iteration not to set size self._all_nodes during iteration
for orphan in orphans:
if orphan not in spanning_line:
spanning_line.insert(0, orphan)
self._all_nodes.remove(orphan)
return spanning_line