Anonymous blocks (PEP 340)

PEP (Python Enhancement Proposal) 340 suggests adding a new block construct to the Python language which would "provide a mechanism for encapsulating patterns of structure". I don't understand the details of the whole proposal just yet, but it looks like the point is making it simpler to execute a blocks of code between other steps, without having to put all the other steps into the code individually. For example, from the PEP, a way to execute some commands while a file is open and guarantee it will be closed when done:

def opening(filename, mode="r"):
    f = open(filename, mode)
    try:
        yield f
    finally:
        f.close()

Used as follows:

block opening("/etc/passwd") as f:
    for line in f:
        print line.rstrip()

Or to retry something several times:

def auto_retry(n=3, exc=Exception):
    for i in range(n):
        try:
            yield None
            return
        except exc, err:
            # perhaps log exception here
            continue
    raise # re-raise the exception we caught earlier

Used as follows:

block auto_retry(3, IOError):
    f = urllib.urlopen("http://python.org/peps/pep-0340.html")
    print f.read()

This seems to me to be trying to solve a problem long ago solved by Lisp's macros, which coincidentally also solve a plethora of other problems unaddressed by the proposed block facility. I'm happy to say Noodle should never need block. (Of course, if a programmer does need it, she can implement it as a macro pretty quickly!)

I see more and more how the capability of extending Lisp's syntax has made it so powerful and so capable of remaining competetive after being around for 50 years.