Roald de Vries wrote:
Hi all,
I have a list that I'm iterating over, and during the iteration items
are appended. Moreover, it is iterated over in two nested loops. If the
inner loop comes to the end, I want the outer loop to append an item. Is
there a way to do this? Because once an iterator has raised a
StopIteration, it can not go to a next item anymore.
Aside question: is there a rationale for the current behavior? To me it
seems more natural to continue iteration after appending new items.
I want to use it for a graph walk.
nodes is a list of all nodes,
edges is an on the fly constructed list of edges in the order of visiting,
initial_nodes is a list of (root) nodes
edges = []
edge_it = iter(edges)
for node in initial_nodes:
edges += node.leaving_edges
try:
while True:
edge = edge_it.next()
edges += edge.head.leaving_edges
except StopIteration:
pass
Thanks in advance, cheers, Roald
You could add the new edges to another list:
edges = []
pending_edges = []
for node in initial_nodes:
pending_edges += node.leaving_edges
while pending_edges:
new_edges = []
for edge in pending_edges:
new_edges += edge.head.leaving_edges
edges += pending_edges
pending_edges = new_edges
or use indexing:
edges = []
for node in initial_nodes:
edges += node.leaving_edges
index = 0
while index < len(edges):
edges += edges[index].head.leaving_edges
index += 1
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