looping over a big file
peter at engcorp.com
Mon Jul 4 03:28:06 CEST 2005
Michael Hoffman wrote:
> Mike Meyer wrote:
>> Guido has made a pronouncement on open vs. file. I think he prefers
>> open for opening files, and file for type testing, but may well be
>> wrong. I don't think it's critical.
> He has said that open() may be used for things other than files in the
> future. So if you want to be sure you're opening a file, use file().
Probably this is the same sort of things as "if you want to be sure your
function is working with an integer, you have to test whether it is an
integer" (or use a statically typed language).
Which is advice that is generally rebutted around here with comments
about "duck typing" (as in, if it acts like an integer, then stop
worrying about what it actually is).
If open() can ever return things other than files, it seems likely it
will do so only under conditions that make it pretty much safe to assume
that existing code will continue to operate "as expected" (note: not
"always with a file").
I'm not going to try to picture just how this might happen, but I could
imagine, for example, some kind of support for protocol prefixes (ala
"http:" or "ftp:"), or perhaps some sort of support for encrypted or
compressed data. Or maybe it would require a prior call to some
function to enable the magic that lets open() return non-files.
If any of that is reasonable, then using open() is actually the better
approach to ensuring your code "does the right thing" in the future, and
"file" should still be used in the rare case where you actually want to
test whether something is a particular type of thing.
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