Recursive list comprehension

[Steven Bethard]

This is a ways off, if ever, but I think the general advice for user code
is to use the newer protocol.

Yes, definitely. I hope no one misconstrued me to be suggesting that
you should use the 'sequence protocol' for iterators (e.g. using
__getitem__ and raising an IndexError). This is deprecated and is only
supported for backwards compatiblity. All new code should define
__iter__ instead.

So, for the purpose of writing new code, I
think it justified to forget about or at least ignore the older iteration
protocol.

This is probably valid as long as you don't need your code to work with
any objects defined before the __iter__ protocol.

Steve

 

[Nick Craig-Wood]

While trying to break your code with a len() > 1 string I noted that strings
don't feature an __iter__ attribute. Therefore obj.__iter__() is not
equivalent to iter(obj) for strings. Do you (plural) know whether this is a
CPython implementation accident or can be relied upon?

I'd like to know this too!

You can write the above as the shorter (and safer IMHO - it doesn't
catch any exceptions it shouldn't)

def flatten( i ):
if hasattr(i, "__iter__"):
for j in i:
for k in flatten(j):
yield k
else:
yield i