> > > To show this on simple example: > > > > >>> from itertools import count, islice > > >>> it = count() > > >>> x, y = it > > >>> it > > count(3) > > For everyone else who was confused by this, as I was, that's not > actually a copy and paste from the REPL. There should be a ValueError > raised after the x, y assignment. As given, it is confusing because it > looks like the assignment succeeded, when in fact it didn't. > > > > Here the count was advanced two times but assignment did not happen. > > Correct, because there was an exception raised. >
Sorry for that, I did not want to embarrass anyone, so I wrote below that the assignment did not happen. But probably the code should speak for itself, especially if it looks like a copy from REPL > if isinstance(it, collections.abc.Iterator): > # special case for iterators > x, y = it > else: > # sequences keep the old behaviour > x, y = it[:2] > No, it can be simply x, y = iter(it) > > Cons: > > 1. A special case of how assignment works > > 2. As with any implicit behavior, hard-to-find bugs > > Right. Hard-to-find bugs beats any amount of convenience in the > interactive interpreter. To use an analogy: > > "Sure, sometimes my car suddenly shifts into reverse while I'm driving > at 60 kph, sometimes the engine falls out when I go around the corner, > and occasionally the brakes catch fire, but gosh the cup holder makes it > really convenient to drink coffee while I'm stopped at traffic lights!" > :-) Perhaps a better idea might be special syntax to tell the interpreter > you don't want to run the right-hand side to completion. "Explicit is > better than implicit" -- maybe something special like: > > x, y, * = iterable > I wrote somewhere above, that "may be I like this form". But for me * '"starred" target implies -> collect something from iterable. So now I'm towards: x, y, ... = iterable But I have not summed up yet what pitfalls can be on this path. Thank you your remarks were very extensive! With kind regards, -gdg
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