code: def to_file(self, f, sorted=True, relativize=True, nl=None):
          if sys.hexversion >= 0x02030000:
              str_type = basestring
          else:
              str_type = str
          if nl is None:
              opts = 'w'
          else:
              opts = 'wb'
          if isinstance(f, str_type):
              f = file(f, opts)
              want_close = True
          else:
              want_close = False
          try:
              if sorted:
                  names = self.keys()
                  names.sort()
              else:
                  names = self.iterkeys()
              for n in names:
                  l = self[n].to_text(n, origin=self.origin,
                                      relativize=relativize)
                  if nl is None:
                      print >> f, l
                  else:
                      f.write(l)
                      f.write(nl)
          finally:
              if want_close:
                  f.close()