title: How do I make a dynamically expanding array in python
body: <p>Ok I have this part of code:</p>
  
  <pre><code>def Reading_Old_File(self, Path, turn_index, SKU):
          print "Reading Old File! Turn Index = ", turn_index, "SKU= ", SKU
          lenght_of_array=0
          array_with_data=[]
          if turn_index==1:
              reading_old_file = open(Path,'rU')
              data=np.genfromtxt(reading_old_file, delimiter="''", dtype=None)
              for index, line_in_data in enumerate(data, start=0):
                  if index&lt;3:
                      print index, "Not Yet"
                  if index&gt;=3:
                      print "&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt; Reading All Old Items"
                      i=index-3
                      old_items_data[i]=line_in_data.split("\t")
                      old_items_data[i]=[lines_old.strip()for lines_old in old_items_data]
                      print old_items_data[i]
                      print len(old_items_data)
  </code></pre>
  
  <p>So what I am doing here is, I'm reading a file, on my first turn, I want to read it all, and keep all data, so it would be something like:</p>
  
  <pre><code>old_items_data[1]=['123','dog','123','dog','123','dog']
  old_items_data[2]=['124','cat','124','cat','124','cat']
  old_items_data[n]=['amount of list members is equal each time']
  </code></pre>
  
  <p>each line of the file should be stored in list, so I can use it in future for comparing, when turn_index will be greater than 2 I'll compare coming line with lines in every list(array) by iterating over all lists.
  So question is how do I do it, or is there any better way to compare lists?
  I'm new to python so maybe someone could help me with this issue? </p>
  
  <p>Thanks</p>