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Generators: section 9.10 of the python tutorial

Peter Otten __peter__ at web.de
Thu May 13 15:38:29 EDT 2004 
David Stockwell wrote:

> Section 9.10 of the tutorial discusses the yield keyword.   When I tried
> using it I get the following SyntaxError.
> 
> What does this error mean?  Does it mean we can't use yield in our code? 

You need the line
from __future__ import generators 
as the first statement in your script (or you can update from Python 2.2.x
to 2.3.x).

> Is yield a form of a 'return' ??

In the context of a for loop, you can indeed think of yield as a kind of
return that stops the execution of the function (reverse() in your example)
but saves its internal state, and on the next iteration resumes execution
at the point where it stopped the last time - until it encounters the next
yield. When the function aka 'generater' terminates, the for loop ends.
(The underlying mechanism is a bit more general, but as generators are used
with for loops in the great majority of cases you shouldn't care until you
are comfortable with the common case as well as classes and exceptions).

Peter
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