> Steven Bethard wrote: >> >>Right. str and unicode objects support iteration through the old >>__getitem__ protocol, not the __iter__ protocol. If you want to use >>something as an iterable, just use it and catch the exception: >> >>try: >> itr = iter(a) >>except TypeError: >> # 'a' is not iterable >>else: >> # 'a' is iterable
Martin Miller broke the order of reading by top-posting:
In either case, you can't tell a string and list apart, which is what the OP wanted to know, namely how to differentiate the two.
Yes, sorry, I should have marked my post OT. It was an answer to Terry Hancock's post suggesting hasattr(x, '__iter__'), not the OP.
Perhaps the test for an __iter__ attribute *is* the way to go because you can tell the difference between the two type.
I've seen this done before, e.g.:
try:
itr = iter(x)
except TypeError:
# is not iterable
else:
if hasattr(x, '__iter__'):
# is other iterable
else:
# is str or unicodeI don't like this idea much because it depends on str and unicode _not_ having a particular function. I haven't seen any guarantee anywhere that str or unicode won't ever grow an __iter__ method. So this code seems dangerous as far as future compatibility goes.
I think the technique suggested by Robin Munn nearly a year ago (and referenced by the link in Simon Brunning's post): http://groups-beta.google.com/group/comp.lang.python/msg/c8befd4bed517bbc namely:
try: a + '' except TypeError: pass else: a= [a]
would be a good usable solution, although it's not totally infallible.
Yup, if I had to do this kind of type-checking (which I don't think I ever do), I'd probably go with something along these lines.
STeVe -- http://mail.python.org/mailman/listinfo/python-list
