def add_edge(self, head_id, tail_id, edge_data=1, create_nodes=True):
"""
Adds a directed edge going from head_id to tail_id.
Arbitrary data can be attached to the edge via edge_data.
It may create the nodes if adding edges between nonexisting ones.
:param head_id: head node
:param tail_id: tail node
:param edge_data: (optional) data attached to the edge
:param create_nodes: (optional) creates the head_id or tail_id node in case they did not exist
"""
# shorcut
edge = self.next_edge
# add nodes if on automatic node creation
if create_nodes:
self.add_node(head_id)
self.add_node(tail_id)
# update the corresponding incoming and outgoing lists in the nodes
# index 0 -> incoming edges
# index 1 -> outgoing edges
try:
self.nodes[tail_id][0].append(edge)
self.nodes[head_id][1].append(edge)
except KeyError:
raise GraphError('Invalid nodes %s -> %s' % (head_id, tail_id))
# store edge information
self.edges[edge] = (head_id, tail_id, edge_data)
self.next_edge += 1
def out_edges(self, node):
"""
Returns a list of the outgoing edges
"""
try:
return list(self.nodes[node][1])
except KeyError:
raise GraphError('Invalid node %s' % node)
return None
def inc_edges(self, node):
"""
Returns a list of the incoming edges
"""
try:
return list(self.nodes[node][0])
except KeyError:
raise GraphError('Invalid node %s' % node)
return None
def edge_by_id(self, edge):
"""
Returns the edge that connects the head_id and tail_id nodes
"""
try:
head, tail, data = self.edges[edge]
except KeyError:
head, tail = None, None
raise GraphError('Invalid edge %s' % edge)
return (head, tail)
def restore_edge(self, edge):
"""
Restores a previously hidden edge back into the graph.
"""
try:
head_id, tail_id, data = self.hidden_edges[edge]
self.nodes[tail_id][0].append(edge)
self.nodes[head_id][1].append(edge)
self.edges[edge] = head_id, tail_id, data
del self.hidden_edges[edge]
except KeyError:
raise GraphError('Invalid edge %s' % edge)
def restore_node(self, node):
"""
Restores a previously hidden node back into the graph and restores
all of its incoming and outgoing edges.
"""
try:
self.nodes[node], all_edges = self.hidden_nodes[node]
for edge in all_edges:
self.restore_edge(edge)
del self.hidden_nodes[node]
except KeyError:
raise GraphError('Invalid node %s' % node)
def hide_node(self, node):
"""
Hides a node from the graph. The incoming and outgoing edges of the
node will also be hidden. The node may be unhidden at some later time.
"""
try:
all_edges = self.all_edges(node)
self.hidden_nodes[node] = (self.nodes[node], all_edges)
for edge in all_edges:
self.hide_edge(edge)
del self.nodes[node]
except KeyError:
raise GraphError('Invalid node %s' % node)
def hide_edge(self, edge):
"""
Hides an edge from the graph. The edge may be unhidden at some later
time.
"""
try:
head_id, tail_id, edge_data = self.hidden_edges[edge] = self.edges[
edge]
self.nodes[tail_id][0].remove(edge)
self.nodes[head_id][1].remove(edge)
del self.edges[edge]
except KeyError:
raise GraphError('Invalid edge %s' % edge)
def __init__(self, edges=None):
"""
Initialization
"""
self.next_edge = 0
self.nodes, self.edges = {}, {}
self.hidden_edges, self.hidden_nodes = {}, {}
if edges is not None:
for item in edges:
if len(item) == 2:
head, tail = item
self.add_edge(head, tail)
elif len(item) == 3:
head, tail, data = item
self.add_edge(head, tail, data)
else:
raise GraphError("Cannot create edge from %s" % (item, ))
def generate_random_graph(node_num, edge_num, self_loops=False, multi_edges=False):
'''
Generates and returns a :py:class:`~altgraph.Graph.Graph` instance with *node_num* nodes
randomly connected by *edge_num* edges.
'''
g = Graph.Graph()
if not multi_edges:
if self_loops:
max_edges = node_num * node_num
else:
max_edges = node_num * (node_num-1)
if edge_num > max_edges:
raise GraphError("inconsistent arguments to 'generate_random_graph'")
nodes = range(node_num)
for node in nodes:
g.add_node(node)
while 1:
head = random.choice(nodes)
tail = random.choice(nodes)
# loop defense
if head == tail and not self_loops:
continue
# multiple edge defense
if g.edge_by_node(head,tail) is not None and not multi_edges:
continue
# add the edge
g.add_edge(head, tail)
if g.number_of_edges() >= edge_num:
break
return g