title: Get path of all .txt files in a folder and subfolders
body: <p>I have to get path of all files from a folder, with a specific extension, let's say .txt ( I thing it's the same for another extension) and put them in a .txt file. The problem is that in the folder, are others folders with other .txt files, and I need the path from them too. 
  I wrote a code, but it's not working for subfolders. Can anybody help?</p>
  
  <pre><code>list1=[]; 
  
  outputFilePath = 'C:\...\playlist.txt'
  
  with open("C:\\...\\folderPath2.txt","r") as f:
      output = f.readline()
  
  
  for dir_, _, files in os.walk(output):
      for fileName in files:
                  relDir = os.path.abspath(output)
                  relFile = os.path.join(relDir, fileName)
                  list1.append(relFile)   
  
  
  with open(outputFilePath, 'r+') as file1:
           for lines in list1:
              file_name, file_extension = os.path.splitext(lines)
              if  (file_extension == '.txt'):
                  file1.writelines(lines)
                  file1.writelines('\n')
  </code></pre>