From: Robert Klemme <shortcutter@...>
Date: 2008-12-17T00:28:02+09:00
Subject: Re: implementing python's os.walk

2008/12/16 Brad Volz <bradv@curmudgeon.net>:
> I seem to be having some difficulty creating a version of python's os.walk()
> for ruby, and I was hoping for some pointers.
>
> As some background, python's os.walk() [1] is a generator function.  It is
> passed the top of a directory tree and it returns the following for each
> subdirectory that it encounters:
>  . the working directory
>  . an Array of subdirectories
>  . an Array of non-directory files
>
> Here is some truncated output for my use case:
>
>>>> import os
>>>> repo = '/usr/local/nfsen/profiles-data/live/lax1er1'
>>>> for root, dirs, files in os.walk(repo):
> ...     if len(files) == 288:
> ...         print root
> ...
> /usr/local/nfsen/profiles-data/live/lax1er1/2008/11/11
>  ..
> /usr/local/nfsen/profiles-data/live/lax1er1/2008/12/13
>
> Essentially, when there are exactly 288 files in a subdirectory, I want to
> print or otherwise do something with the working directory.

> The part that I think is totally wrong is:
>
>        for o in find_dirs(d) { |a,b,c| puts "#{a} #{b} #{c}"}
>
> It's really only in there currently to keep the from getting
> 'LocalJumpError: no block given.'  Unfortunately, I have no idea what the
> correct way to deal with this would be.
>
> The missing part would be including the directory contents in addition to
> the working directory and the Array of subdirectories.
>
> So, I guess my main questions would be:  What do I need to do to get this
> sort of a generator to work?  Do I need to wrap this up in a 'class' or is a
> 'def' sufficient?  What should the block look like, and where should it be
> in the code?

You have a recursive algorithm here but you want each call of the
method invoke the *same block*.  This can be achieved by forwarding
the block with the &b notation:

def find_dirs(top, &b)
  ...
  # enter recursion
  find_dirs(d, &b)
end

The way you did it, every invocation yields to the caller's block
which is only the correct one for the first caller; all others yield
to the block in their parent calling find_dirs.

You might as well be able to create a totally different solution using Find:

require 'find'

roots.each do |root|
  dir_count = Hash.new 0

  Find.find root do |file|
    d, f = File.split file
    next if /\A\.{1,2}\z/ =~ f
    dir_count[d] += 1 if File.file? file
  end

  dir_count.each do |dir, cnt|
    puts root if cnt == 288
  end
end

Kind regards

robert

-- 
remember.guy do |as, often| as.you_can - without end