title: Why does Python CSV module make the CSV file read-only when I try to open it after running program?
body: <p>I'm using a program (follows) to see the similarities in certain columns between two CSV files, then create a third when data matches certain specifications (two columns are the same but the third is not) so that I can update an e-mail list.</p>
  
  <p>When I try to open the results.csv file after running the program however, Windows Excel will only open the program in read-only mode.</p>
  
  <p>Any thoughts?</p>
  
  <p>Here's my code:</p>
  
  <pre><code>import csv
  
  sample_data = open("sample.csv", "r")
  lib_data = open("library.csv", "r")
  csv1 = csv.reader(sample_data)
  csv2 = csv.reader(lib_data)
  
  results = open("results.csv", "w")
  res_csv = csv.writer(results)
  
  limit = 1071
  limit2 = 1001
  
  x = 0
  y = 0
  
  while (y != limit):
      row1 = csv1.__next__()
      while (x != limit2):
          row2 = csv2.__next__()
          if (row1[0] == row2[3] and row1[1] == row2[2] and row1[2] != row2[5]):
              print ("SAMPLE:")
              print (row1[0], ", ", row1[1], ", ", row1[2])
              print ("LIBRARY:")
              print (row2[3], ", ", row2[2], ", ", row2[5])
              print("\n")
              res_csv.writerow(row1)
          x = x+1
      y = y+1
      x = 0
      lib_data.seek(0)
  </code></pre>