Occasionally I implement an algorithm recursively then hit the recursion limit in Python.

For example, I just wrote this:

def clique(self, node, done=None): if done is None: done = set() done.add(node) for other_node in self.edges_by_node[node]: if other_node not in done: self.clique(other_node, done) return done

which hits a limit if the graph is too big.

So I rewrote it like this:

def clique(self, start_node): done = set() to_do = [start_node] while to_do: node = to_do.pop() done.add(node) for other_node in self.edges_by_node[node]: if other_node not in done: to_do.append(other_node) return done

There's a simple relationship between the two, quite independent of the specific task at hand. Which got me thinking about abstracting the specific task out of the recursive versus non-recursive pattern.

I guess I was having an SICP moment :-)