title: open .tar.gz archives in python
body: <p>,i've got an issue with this pair of lines, coded in Python:</p>
  
  <pre><code>#File name spacchetta_N_zip.py
  
  import tarfile
  import gzip
      with tarfile.TarFile.open(i, 'r:gz') as tarredgzippedFile:
                          tarredgzippedFile.extractall(cartella)
  </code></pre>
  
  <p>I'm sure i'm opening a .tar.gz archive.</p>
  
  <p>I really don't know what's wrong, i've surfed the web and this would work... but i got this error:</p>
  
  <pre><code>File "spacchetta_N_zip.py", line 70, in Spacchetta
      with tarfile.TarFile.open(i, 'r:gz') as tarredgzippedFile:
    File "/usr/lib/python2.7/tarfile.py", line 1678, in open
      return func(name, filemode, fileobj, **kwargs)
    File "/usr/lib/python2.7/tarfile.py", line 1729, in gzopen
      raise ReadError("not a gzip file")
  tarfile.ReadError: not a gzip file
  </code></pre>
  
  <p>Help me please</p>