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"""Simplistic implementation of a graph"""
__all__ = ('Node', 'Graph')
class Node(object):
"""A Node in the graph. They know their neighbours, and have an id which should
resolve into a string"""
__slots__ = ('in_nodes', 'out_nodes', 'id')
def __init__(self, id=None):
self.id = id
self.in_nodes = list()
self.out_nodes = list()
def __str__(self):
return str(self.id)
def __repr__(self):
return "%s(%s)" % (type(self).__name__, self.id)
class Graph(object):
"""A simple graph implementation, keeping nodes and providing basic access and
editing functions. The performance is only suitable for small graphs of not
more than 10 nodes !"""
__slots__ = "nodes"
def __init__(self):
self.nodes = list()
def __del__(self):
"""Deletes bidericational dependencies"""
for node in self.nodes:
node.in_nodes = None
node.out_nodes = None
# END cleanup nodes
# otherwise the nodes would keep floating around
def add_node(self, node):
"""Add a new node to the graph
:return: the newly added node"""
self.nodes.append(node)
return node
def remove_node(self, node):
"""Delete a node from the graph
:return: self"""
try:
del(self.nodes[self.nodes.index(node)])
except ValueError:
return self
# END ignore if it doesn't exist
# clear connections
for outn in node.out_nodes:
del(outn.in_nodes[outn.in_nodes.index(node)])
for inn in node.in_nodes:
del(inn.out_nodes[inn.out_nodes.index(node)])
node.out_nodes = list()
node.in_nodes = list()
return self
def add_edge(self, u, v):
"""Add an undirected edge between the given nodes u and v.
return: self
:raise ValueError: If the new edge would create a cycle"""
if u is v:
raise ValueError("Cannot connect a node with itself")
# are they already connected ?
if u in v.in_nodes and v in u.out_nodes or \
v in u.in_nodes and u in v.out_nodes:
return self
# END handle connection exists
# cycle check - if we can reach any of the two by following either ones
# history, its a cycle
for start, end in ((u, v), (v,u)):
if not start.in_nodes:
continue
nodes = start.in_nodes[:]
seen = set()
# depth first search - its faster
while nodes:
n = nodes.pop()
if n in seen:
continue
seen.add(n)
if n is end:
raise ValueError("Connecting u with v would create a cycle")
nodes.extend(n.in_nodes)
# END while we are searching
# END for each direction to look
# connection is valid, set it up
u.out_nodes.append(v)
v.in_nodes.append(u)
return self
def input_inclusive_dfirst_reversed(self, node):
"""Return all input nodes of the given node, depth first,
It will return the actual input node last, as it is required
like that by the pool"""
stack = [node]
seen = set()
# depth first
out = list()
while stack:
n = stack.pop()
if n in seen:
continue
seen.add(n)
out.append(n)
# only proceed in that direction if visitor is fine with it
stack.extend(n.in_nodes)
# END call visitor
# END while walking
out.reverse()
return out
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