title: sqlite3 in Python: Update a column in one table through a column from another table when the primary key is the same
body: <p>I want to use sqlite3 in Python. I have a table with four columns (id INT, other_no INT, position TEXT, classification TEXT, PRIMARY KEY is id). In this table, the column  for classification is left empty and will be updated by the information from table 2. See my code below. I then have a second table which has three columns. (id INT, class TEXT, type TEXT, PRIMARY KEY (id)). Basically, the two tables have two common columns. In both tables, the primary key is the id column, the classification and class column would eventually have to be merged. So the code needs to be able to go through table 2 and whenever it finds a matching id in table 1 to updating the class column (of table 1) from the classification column of table 2. The information to build the two tables comes from two separate files. </p>
  
  <pre><code># function to create Table1...
  # function to create Table2... 
  </code></pre>
  
  <p>(the tables are created as expected). The problem occurs when I try to update table1 with information from table2. </p>
  
  <pre><code>def update_table1():
      con = sqlite3.connect('table1.db', 'table2.db')  #I know this is wrong but if how do I connect table2 so that I don't get error that the Table2 global names is not defined? 
  
      cur = con.cursor()
      if id in Table2 == id in Table1:
          new_classification = Table2.class # so now instead of Null it should have the class information from table2
      cur.execute("UPDATE Table1 SET class = ? WHERE id =? ", (new_classification, id))
      con.commit()
  </code></pre>
  
  <p>But, I get an error for line2: TypeError: a float is required. I know that it's because I put two parameters in the connect method. But then if I only connect with Table1 I get the error Table2 is not defined. </p>
  
  <p>I read this post <a href="https://stackoverflow.com/questions/12267329/updating-a-column-in-one-table-through-a-column-in-another-table">Updating a column in one table through a column in another table</a> I understand the logic around it but I can't translate the SQL code into Python. I have been working on this for some time and can't seem to just get it. Would you please help? Thanks </p>
  
  <p>After the comments of a user I got this code but it still doesn't work: </p>
  
  <pre><code>#connect to the database containing the two tables 
  cur.execute("SELECT id FROM Table1")
  for row in cur.fetchall():
      row_table1 = row[0]
  
  cur.execute("SELECT (id, class) FROM Table2")
  for row1 in cur.fetchall():
      row_table2 = row[0]    #catches the id
      row_table2_class = row[1]    #catches the name
  if row_table1 == row_table2:
      print "yes"               #as a test for me to see the loop worked
      new_class = row_table_class
  cur.execute("UPDATE Table1 SET classification=? WHERE id=?", (new_class, row_table1))
  con.commit()
  </code></pre>
  
  <p>From this however I get an operational error. I know it's my syntax, but like I said I am new to this so any guidance is greatly appreciated. </p>