title: Parsing my string to int is causing ValueError in python
body: <p>For some reason int(str) is causing an error. I can't work out why. I'm wondering if someone can tell me why.</p>
  
  <pre><code>cx4_list_reduce = ['[#1]',(1,3,5),(7,6,9)]
  list2= ['[#2]',(2,5,4), (1,3,5), (5,8,1), (7,2,6)]
  n2 =3
  for process_tuple in cx4_list_reduce:
        d_num = ""
        if process_tuple == list2[0]:
              d_num = process_tuple[2:3]
        n1 = int(d_num)
        if n1 &lt;= n2:
             print('n1 =&lt; n2')
             continue
        else:
              print('n1 =&gt; n2')
  </code></pre>
  
  <p>Error: <code>invalid literal for int() with base 10: ''</code></p>