[Python-ideas] Revised^4 PEP on yield-from

Adam Olsen rhamph at gmail.com
Fri Feb 20 01:50:26 CET 2009

On Thu, Feb 19, 2009 at 5:24 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Traversing a binary tree with a non-generator:
>  def traverse(node):
>    if node:
>      process_node(node)
>      traverse(node.left)
>      traverse(node.right)
> Traversing it with a generator:
>  def traverse(node):
>    if node:
>      yield process_node(node)
>      yield from traverse(node.left)
>      yield from traverse(node.right)
> Do you still think an unrolled version would be
> equally clear? If so, you have extremely different
> tastes from me!

This is a pretty good example, IMO.

However, I'd like to see what a trampoline would look like to support
something like this:

def traverse(node):
    if node:
        yield leaf(process_node(node))
        yield traverse(node.left)
        yield traverse(node.right)

If the use case is sufficiently common we can consider putting such a
trampoline in the stdlib.  If not it should at least go in the

And FWIW, a C implementation of such a trampoline should be almost
identical to what the PEP proposes.  It's just substituting a type
check for the new syntax.

Adam Olsen, aka Rhamphoryncus

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