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class DirectedGraph(object):
"""A graph structure with directed edges.
"""
def __init__(self):
self._vertices = set()
self._forwards = {} # <key> -> Set[<key>]
self._backwards = {} # <key> -> Set[<key>]
def __iter__(self):
return iter(self._vertices)
def __len__(self):
return len(self._vertices)
def __contains__(self, key):
return key in self._vertices
def copy(self):
"""Return a shallow copy of this graph.
"""
other = DirectedGraph()
other._vertices = set(self._vertices)
other._forwards = {k: set(v) for k, v in self._forwards.items()}
other._backwards = {k: set(v) for k, v in self._backwards.items()}
return other
def add(self, key):
"""Add a new vertex to the graph.
"""
if key in self._vertices:
raise ValueError("vertex exists")
self._vertices.add(key)
self._forwards[key] = set()
self._backwards[key] = set()
def remove(self, key):
"""Remove a vertex from the graph, disconnecting all edges from/to it.
"""
self._vertices.remove(key)
for f in self._forwards.pop(key):
self._backwards[f].remove(key)
for t in self._backwards.pop(key):
self._forwards[t].remove(key)
def connected(self, f, t):
return f in self._backwards[t] and t in self._forwards[f]
def connect(self, f, t):
"""Connect two existing vertices.
Nothing happens if the vertices are already connected.
"""
if t not in self._vertices:
raise KeyError(t)
self._forwards[f].add(t)
self._backwards[t].add(f)
def iter_edges(self):
for f, children in self._forwards.items():
for t in children:
yield f, t
def iter_children(self, key):
return iter(self._forwards[key])
def iter_parents(self, key):
return iter(self._backwards[key])