tjreedy at udel.edu
Thu Aug 7 09:01:38 CEST 2003
"Jeremy Fincher" <firstname.lastname@example.org> wrote in message
news:bgsqj5$228$1 at news.cis.ohio-state.edu...
> Sometimes I find myself simply wanting the length of an iterator.
An iterator is a function/method that traverses (or possibly
generates) a seqeuence. The sequence has a length (actual or
potential) but the iterator does not.
> For example, to collect some (somewhat useless ;))
> statistics about a program of mine, I've got code like this:
> objs = gc.get_objects()
> classes = len([obj for obj in objs if inspect.isclass(obj)])
> functions = len([obj for obj in objs if
> modules = len([obj for obj in objs if
> dicts = len([obj for obj in objs if type(obj) ==
> lists = len([obj for obj in objs if type(obj) ==
> tuples = len([obj for obj in objs if type(obj) ==
Alternative: initialize six counters to 0. Scan list once and update
> Now, obviously I can (and will, now that 2.3 is officially released
> replace the list comprehensions with itertools.ifilter, but I need
> itertools.ilen to find the length of such iterators.
You mean the associated sequence.
> I can imagine such a need arises in more useful situations than
> this is the particular case that brought the need to mind.
> The Python code is simple, obviously:
> def ilen(iterator):
> i = 0
> for _ in iterator:
> i += 1
> return i
> But it's a pity to use itertools' super-fast iterators and have to
> raw Python to determine their length :)
If you mean a c-coded counter (which would not be an iterator itself)
equivalent to the above, that could be done. Perhaps len() could be
upgraded/extended to accept an iterator and count when it can't get a
__len__ method to call. The main downside is that iterators are
sometimes destructive (run once only).
In the meanwhile, is this really a bottleneck for you? or merely the
'pity' of a program running in 1 sec when 0.1 is possible?
Terry J. Reedy
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