On Dec 14, 2019, at 21:52, David Mertz <[email protected]> wrote:
>
> A pattern I've written a number of times is roughly:
>
> lines = open(fname)
> header = next(lines)
> for line in lines:
> process (line, header)
>
> That's not so artificial, I think. Of course, first() would also work here.
> But I'm not sure it's any particular advantage in this case.
I think first is actually worse here. If you might ever refactor this code to,
say, take an arbitrary iterable as input rather than opening (and leaking) a
file by name, using next means that forgetting to call iter somewhere is an
easy to debug TypeError, but using first means it’s a subtle bug where the
header is counted again as a normal row.
But I also don’t think anyone will reach for first here. People who are already
thinking of the file in terms of being an iterable are going to continue to use
next. Everyone else is just going to call readline instead of either next or
first.
I think the advantages are in cases like the one Chris pointed out, where you
have a dict view (or some other case where you know you have a non-iterator
iterable but it isn’t, or at least might not be, a sequence), where first is
helpful, for the reasons he described.
For example, you’re at the REPL interactively working out how to process some
web service:
>>> p = requests.post(url)
>>> r = p.json()
>>> first(r.items())
... here I see what I need to deal with
Or maybe even that ends up bigger than you expected, but then you write:
>>> things = _['things']
>>> things[0]
... still too big? ...
>>> thing = things[0]
>>> first(thing.items())
... aha, now I get it
Looking at my own REPL history and pile of throwaway scripts, dicts actually
seem to make up a lot of my own uses of more_itertools.first.
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