Re: Test for structure

[Steven Bethard]

Terry Hancock wrote:
> But you probably shouldn't do that. You should probably just test to
> see if the object is iterable --- does it have an __iter__ method?
>
> Which might look like this:
>
> if hasattr(a, '__iter__'):
>     print "'a' quacks like a duck"
Martin Miller top-posted:
I don't believe you can use the test for a __iter__ attribute in this
case, for the following reason:
c1 = 'abc'
c2 = ['de', 'fgh', 'ijkl']
hasattr(c1, '__iter__')
False
hasattr(c2, '__iter__')
True
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
Another lesson in why EAPF is often better than LBYL in Python[1].
STeVe
[1] http://www.python.org/moin/PythonGlossary
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