Re: Graph library for Python (was: Re: python bijection)

On Mon, Dec 7, 2009 at 5:48 PM, Steven D'Aprano
<steve@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Mon, 07 Dec 2009 17:23:24 -0500, geremy condra wrote:


 * Graph.__iter__ could be mapped to an iterator using
  the fastest traversal method for the graph nodes (ie. order does not
  matter, it's only important that all nodes are found as fast as
  possible)

Again, it seems ambiguous as to whether nodes or edges are the intended
target here, and while the API can obviously dictate that, it seems a
bit like a case of "in the face of ambiguity, refuse the temptation to
guess" to me.

Consider dicts. They have methods that iterates over keys, values, and
(key, value) pairs, but if you just iterate over the dict itself, you get
the keys. This was a deliberate design decision.

It's not a matter of guessing in the face of ambiguity, but giving an
easy way to get the most common case. Assuming that iteration over nodes
is more common than iteration over edges, then iter(graph) should yield
nodes in some unspecified order. If you need the nodes in a particular
order, then you will call some method that guarantees the order, and if
you want the edges, you call a method that gives edges.

If you're not sure whether wanting nodes or edges will be more common,
then you should wait until you, or the community, has more real-world
experience with the module. Python had dicts for something approaching a
decade before they became directly iterable.

I don't have a problem with adding this if there's a strong desire for it,
but at the moment I'm leaning towards a wait-and-see approach, for
all the reasons you described.

Geremy Condra
.

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