title: Exclude ".txt" files
body: <p>I want to exclude ".txt" files of a directory with a regex (and only regex). But this code doesn't work and I don't understand why.
  I have this list :</p>
  
  <pre><code>['/var/tmp/COMMUN/4.1.0_41/Apache',
   '/var/tmp/COMMUN/4.1.0_41/META-INF', 
   '/var/tmp/COMMUN/4.1.0_41/RewriteRules',
   '/var/tmp/COMMUN/4.1.0_41/Robots', 
   '/var/tmp/COMMUN/4.1.0_41/smokeTest',
   '/var/tmp/COMMUN/4.1.0_41/tutu.txt']
  </code></pre>
  
  <p>And I'm trying this code</p>
  
  <pre><code># list_dit is a personal function
  list_dir(toto, filter_function=lambda x: re.match("^.*(?!txt)$", x))
  </code></pre>
  
  <p>Anyone look what is wrong ?</p>