python os.path.walk can't open file
<pre><code>import os
from os.path import splitext,basename
import sys
from lxml import etree

#clean out old files
def cleanBrds(args, dirname,files):
    print "checking "+dirname
    for file in files:
        if file.endswith("_pyclean.brd"):
            if os.path.exists(file):
                print "removing "+file
                os.remove(file)

#prep files
def sanBrds(args, dirname,files):
    print "checking "+dirname
    for file in files:
        if file.endswith(".brd"):
            print "found "+file
            newfile = splitext(basename(file))[0]+"_pyclean.brd"
            tree=etree.parse(file)
            for elem in tree.xpath('//signal'):
                elem.getparent().remove(elem)
            f=open(newfile,'w')
            f.write(etree.tostring(tree))
            f.close();

base_dir="."
os.path.walk(base_dir,cleanBrds,None)
os.path.walk(base_dir,sanBrds,None)
</code></pre>

<blockquote>
<pre><code># python prepbrd.py
checking .
checking ./naut
checking .
found erct.brd
checking ./naut
found nautctrl.brd
Traceback (most recent call last):
  File "prepbrd.py", line 43, in &lt;module&gt;
    os.path.walk(base_dir,sanBrds,None)
  File "/usr/lib/python2.6/posixpath.py", line 236, in walk
    walk(name, func, arg)
  File "/usr/lib/python2.6/posixpath.py", line 228, in walk
    func(arg, top, names)
  File "prepbrd.py", line 22, in sanBrds
    tree=etree.parse(file)
  File "lxml.etree.pyx", line 2706, in lxml.etree.parse (src/lxml/lxml.etree.c:49958)
  File "parser.pxi", line 1500, in lxml.etree._parseDocument (src/lxml/lxml.etree.c:71797)
  File "parser.pxi", line 1529, in lxml.etree._parseDocumentFromURL (src/lxml/lxml.etree.c:72080)
  File "parser.pxi", line 1429, in lxml.etree._parseDocFromFile (src/lxml/lxml.etree.c:71175)
  File "parser.pxi", line 975, in lxml.etree._BaseParser._parseDocFromFile (src/lxml/lxml.etree.c:68173)
  File "parser.pxi", line 539, in lxml.etree._ParserContext._handleParseResultDoc
</code></pre>
  
  <p>(src/lxml/lxml.etree.c:64257)
        File "parser.pxi", line 625, in lxml.etree._handleParseResult (src/lxml/lxml.etree.c:65178)
        File "parser.pxi", line 563, in lxml.etree._raiseParseError (src/lxml/lxml.etree.c:64493)
      IOError: Error reading file 'nautctrl.brd': failed to load external entity "nautctrl.brd"</p>
</blockquote>

<p>I'm fairly new to this, but it seems i may not be passing the parameters correctly from os.path.walk to the other functions.  I want to remove all files ending in _pyclean.brd first, then operate on the remaining .brd files (which are xml).  The functions work fine in a flat directory, but recursively i get the above error.</p>
