Is it an iterator? (was Re: FixedPoint)

[Aahz Maruch]

In article <GJS88.49612$3J1.1396553 at news2.tin.it>,
Alex Martelli  <aleax at aleax.it> wrote:
>
>"something is iterable" if and only if you can iterate on it.  So, try 
>iterating on it, and handle the resulting exception should it turn out
>you can't.  I'm not sure exactly what exceptions would be raised by
>various versions of Python -- probably a TypeError, but one never
>knows -- better to experiment on all relevant versions, or maybe, just
>for once, a generic try/except is acceptable.  An almost acceptable
>version might therefore be:
>
>def isIterable(x):
>    try:
>        for i in x: return 1   # iterable
>        else: return 1         # iterable, although empty
>    except:
>        return 0
>
>Unfortunately, if we're in Python 2.2 and x is an iterator, isIterable
>"consumes" x's first item.  This isn't hard to fix:
>
>def isIterable(x):
>    try: x=iter(x)
>    except: pass
>    else: return 1
>    try:
>        for i in x: return 1   # iterable
>        else: return 1         # iterable, although empty
>    except:
>        return 0

This still breaks with files, I believe (don't have 2.2 handy to test).
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