title: cx_oracle executemany is not inserting all fields
body: <p>I am trying to use cx_oracle executemany to bulk insert rows into an Oracle database table. </p>
  
  <p>My problem is executemany is 'skipping' certain fields without throwing an error and I'm tearing my hair out trying to  understand why. </p>
  
  <p>The values I want to insert are stored in a list: </p>
  
  <pre><code>print (parsed_results[0]) 
  ['100700000005', '00000005006', '20180223', 'Transaction Deposit 1', '1', '', 'N'] 
  print (parsed_results[1])
  ['100700000005', '00000005006', '20180223', 'Transaction Deposit 2', '1', '', 'N'] 
  etc
  </code></pre>
  
  <p>If I loop through the list and insert them one at a time, everything works fine. However when I use executemany certain fields are skipped almost randomly.  </p>
  
  <p>code: </p>
  
  <pre><code>connectString = 'user/password@{dba}'.format(dba=dbname)
  connection = cx_Oracle.connect(connectString)
  cursor = connection.cursor()
  cursor.arraysize = 5000
  s_sql_insert = '''INSERT INTO My_Schema.My_table(
      ID, ACCT_ID, DATE, TYPE,COUNT, REF_NO, REV) 
      VALUES (:ID, :ACCT_ID, :DATE, :TRAN, :COUNT, :REF_NO, :REV)'''
  
  try:
      cursor.prepare(s_sql_insert)
  except Exception as e: 
      logging.error ('Failed to prepare cursor!')
      logging.error('Reason: %s', e)
  
  try:
      cursor.executemany(None, (parsed_results))
  except cx_Oracle.DatabaseError as e:
      logging.error ('Failed to insert rows!')
      logging.error('Reason: %s', e)
  connection.commit()
  cursor.close()
  connection.close()
  </code></pre>
  
  <p>Does anyone know why this is happening or how I can get more information on any errors? </p>