Yield in a recursive function

user_487855 0
Viewed 13829

I am trying to do something to all the files under a given path. I don't want to collect all the file names beforehand then do something with them, so I tried this:

import os
import stat

def explore(p):
  s = ''
  list = os.listdir(p)
  for a in list:
    path = p + '/' + a
    stat_info = os.lstat(path )
    if stat.S_ISDIR(stat_info.st_mode):
     explore(path)
    else:
      yield path

if __name__ == "__main__":
  for x in explore('.'):
    print '-->', x

But this code skips over directories when it hits them, instead of yielding their contents. What am I doing wrong?

directory-structure yield recursion iterator python
9 Answers

os.walk is great if you need to traverse all the folders and subfolders. If you don't need that, it's like using an elephant gun to kill a fly.

However, for this specific case, os.walk could be a better approach.

user_7452940

To answer the original question as asked, the key is that the yield statement needs to be propagated back out of the recursion (just like, say, return). Here is a working reimplementation of os.walk(). I'm using this in a pseudo-VFS implementation, where I additionally replace os.listdir() and similar calls.

import os, os.path
def walk (top, topdown=False):
    items = ([], [])
    for name in os.listdir(top):
        isdir = os.path.isdir(os.path.join(top, name))
        items[isdir].append(name)
    result = (top, items[True], items[False])
    if topdown:
        yield result
    for folder in items[True]:
        for item in walk(os.path.join(top, folder), topdown=topdown):
            yield item
    if not topdown:
        yield result
user_49138100
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