Iterating over files of a huge directory

MRAB python at
Mon Dec 17 19:29:46 CET 2012

On 2012-12-17 17:27, Paul Rudin wrote:
> Chris Angelico <rosuav at> writes:
>> On Tue, Dec 18, 2012 at 2:28 AM, Gilles Lenfant
>> <gilles.lenfant at> wrote:
>>> Hi,
>>> I have googled but did not find an efficient solution to my
>>> problem. My customer provides a directory with a huuuuge list of
>>> files (flat, potentially 100000+) and I cannot reasonably use
>>> os.listdir(this_path) unless creating a big memory footprint.
>>> So I'm looking for an iterator that yields the file names of a
>>> directory and does not make a giant list of what's in.
>> Sounds like you want os.walk.
> But doesn't os.walk call listdir() and that creates a list of the
> contents of a directory, which is exactly the initial problem?
>> But... a hundred thousand files? I know the Zen of Python says that
>> flat is better than nested, but surely there's some kind of directory
>> structure that would make this marginally manageable?
> Sometimes you have to deal with things other people have designed, so
> the directory structure is not something you can control. I've run up
> against exactly the same problem and made something in C that
> implemented an iterator.
<Off topic>
Years ago I had to deal with an in-house application that was written
using a certain database package. The package stored each predefined
query in a separate file in the same directory.

I found that if I packed all the predefined queries into a single file
and then called an external utility to extract the desired query from
the file every time it was needed into a file for the package to use,
not only did it save a significant amount of disk space (hard disks
were a lot smaller then), I also got a significant speed-up!

It wasn't as bad as 100000 in one directory, but it was certainly too
</Off topic>
> It would probably be better if listdir() made an iterator rather than a
> list.

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