title: Get length of csv file without ruining reader?
body: <p>I am trying to do the following:</p>
  
  <pre><code>reader = csv.DictReader(open(self.file_path), delimiter='|')
  reader_length = sum([_ for item in reader])
  for line in reader:
      print line
  </code></pre>
  
  <p>However, doing the <code>reader_length</code> line, makes the reader itself unreadable. Note that I do not want to do a <code>list()</code> on the reader, as it is too big to read on my machine entirely from memory.</p>