Reinhold Birkenfeld <[EMAIL PROTECTED]> wrote: ... > > Using ips[:] to make a copy on the fly is very idiomatic, but I've never > > liked it, personally. I see no reason to prefer it to the even shorter > > and arguably less obscure ips*1, for example. > > "Less obscure"? Either you know the `lst[:]' idiom, or you don't. If you > do, it's fine, if you don't, you will have to look it up to understand > its meaning, and that's a good thing.
I disagree. > Using `lst*1', on the other hand, does not make clear that a copy is > created. If you don't already know what it does, you may assume that > `lst' is left alone. And indeed it is -- whatever object is bound to the name 'lst' is not modified in the least (neither would it be by slicing lst[:], of course). But the RESULT of x*1 is a DISTINCT object from x whenever it matters -- i.e., whenever x is mutable. x[:] *MIGHT* not be a distinct, separate, independent copy if x is, e.g. a Numeric.array: x = Numeric.arange(7) y = x[:] x[3]=23 now y is modified too. Change the middle statement into 'y = x*1', and the third statement won't alter y. So, *WHAT ON EARTH* could possibly make this weird 'x[:]' form preferable to 'x*1'?! It's MUCH more obvious that the second one returns an independent, separate object initially equal to x -- because it does so in many more cases than those in which x[:] does it! I'm not arguing FOR x*1 -- I'm arguing AGAINST x[:] as being even remotely acceptable. > > My preference is: > > > > for ip in list(ips): > > That is the most intriguing variant, of course. It's very down to earth because the result is obviously a list, whatever 'ips' might turn out to be -- no mystery there, and thus, no intrigue. Maybe we should have a simpler way to specify ``an iterator that is INDEPENDENT from any possible changes in the iterable we're passing'', for this specific use case -- but we don't, and I don't think that copy.copy(ips) is a substantial improvement (it would fail when ips is a file, or a generator-iterator, or many other kinds of iterators, for example). list(ips) may do more work than necessary (e.g., if ips were a tuple) but at least its semantics are quite plain and obvious. Alex -- http://mail.python.org/mailman/listinfo/python-list
