[Python-iterators] RE: PEP 255: Simple Generators

[Michael Hudson]

(I'm following up in an odd place for no good reason, in case you have
a mail client that can tell and were wondering).

I think the PEP could use a little discussion about the interactions
between yielding and try/except/finally blocks.  What actually happens
is the only plausible behaviour, but I'm not sure I'd see that if I
wasn't already pretty familiar with Python internals.

Here's a fun example if you're on Unix:

->> import termios, tty, select, errno, os
/>> def gen():
|..     try:
|..         term = termios.tcgetattr(0)
|..         tty.setraw(0)
|..         while 1:
|..             try:
|..                 r, w, e = select.select([0],[],[])
|..                 if 0 in r:
|..                     c = os.read(0,1)
|..                     if c == '\004': # control-D
|..                         return
|..                     else:
|..                         yield c
|..             except OSError, err:
|..                if err.errno == errno.EINTR:
|..                    pass
|..                else:
|..                    return
|..     finally:
|..         termios.tcsetattr(0, termios.TCSADRAIN, term)
\__ 

"list(gen)" is a good way to drive it; type that and batter some keys,
then press control-d.

Arguably the try/finally should be around the call to os.read, and not
contain the yield.  It depends on what you're doing with the generator
I guess.

Also:

->> import keyword
->> 'yield' in keyword.kwlist
0

But, generally speaking, I like.

Cheers,
M.