I want to extract a .tgz file and extract any subdirectories that have files that are .tgz and .tar

I'm using the code below to extract .tgz files. The type of log files (.tgz) that I need to extract have sub-directories that have other .tgz files and .tar files inside them. I want to extract those too.

Ultimately, I'm trying to search for certain strings in all .log files and .txt files that may appear in a .tgz file.

Below is the code that I'm using to extract the .tgz file. I've been trying to work out how to extract the sub-files (.tgz and .tar). So far, I've been unsuccessful.

import os, sys, tarfile

try:
    tar = tarfile.open(sys.argv[1] + '.tgz', 'r:gz')
    for item in tar:
        tar.extract(item)
    print 'Done.'
except:
    name = os.path.basename(sys.argv[0])
    print name[:name.rfind('.')], '<filename>'