The traceback and its context for the exception raised in Python 2.7 is:

...
################################################################################################### 99 %
################################################################################################### 99 %
#################################################################################################### 100 %
Done retrieving 'ftp://ftp.gnome.org/pub/debian/dists/stable/main/source/Sources.bz2'; read 4539023 bytes
Start retrieving 'ftp://ftp.gnome.org/pub/debian/dists/stable/main/source/Sources.bz2'
Start retrieving 'ftp://ftp.gnome.org/pub/debian/dists/stable/main/source/Sources.bz2'
Retrieval of 'ftp://ftp.gnome.org/pub/debian/dists/stable/main/source/Sources.bz2' failed with error: [Errno ftp error] 200 Switching to Binary mode.
Traceback (most recent call last):
  File "urllibftpbug-non-interactive.py", line 62, in _getTask
    self._fromFile = urllib.urlopen(self.fromURL)
  File "/home/schwa/sd/python/cpython/Lib/urllib.py", line 84, in urlopen
    return opener.open(url)
  File "/home/schwa/sd/python/cpython/Lib/urllib.py", line 205, in open
    return getattr(self, name)(url)
  File "/home/schwa/sd/python/cpython/Lib/urllib.py", line 548, in open_ftp
    (fp, retrlen) = self.ftpcache[key].retrfile(file, type)
  File "/home/schwa/sd/python/cpython/Lib/urllib.py", line 886, in retrfile
    conn = self.ftp.ntransfercmd(cmd)
  File "/home/schwa/sd/python/cpython/Lib/ftplib.py", line 326, in ntransfercmd
    host, port = self.makepasv()
  File "/home/schwa/sd/python/cpython/Lib/ftplib.py", line 304, in makepasv
    host, port = parse227(self.sendcmd('PASV'))
  File "/home/schwa/sd/python/cpython/Lib/ftplib.py", line 790, in parse227
    raise error_reply, resp
IOError: [Errno ftp error] 200 Switching to Binary mode.
Total bytes: 4539023
 0 %
 0 %
 0 %
...

I printed the traceback by adding traceback.print_exc() at the end of the _getTask method:

        except Exception, e:
            self._cleanup(e)
            traceback.print_exc()