Stephen Lacy added the comment:
okay, found the documentation I was looking for here:
http://docs.python.org/reference/expressions.html#yield-expressions
which appears to be copied and pasted and modified version of the docs here:
http://docs.python.org/reference/simple_stmts.html#grammar
New submission from Stephen Lacy :
There's reasonable documentation of the yield statement for most python
versions under Section 6: Simple Statements, particularly 6.8 "The Yield
Statement"
(http://docs.python.org/release/2.7/reference/simple_stmts.html#the-yield-statement)