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From: Roald de Vries on 7 Aug 2010 09:57 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
From: MRAB on 7 Aug 2010 14:12
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 |