fixup! trace: use temporary connections to the database

This fixes commit 575a5354.

my2to3/tests/__init__.py

 from lib2to3.tests.test_fixers import FixerTestCase as lib2to3FixerTestCase
 import sqlite3
 
-from my2to3.trace import conn, get_data, tracing_functions
+from my2to3.trace import connection, get_data, tracing_functions
 
 
 class FixerTestCase(lib2to3FixerTestCase):
@@ -10,7 +10,7 @@ class FixerTestCase(lib2to3FixerTestCase):
     super(FixerTestCase, self).setUp(fix_list, fixer_pkg, options)
 
     # Clear the database
-    with conn:
+    with connection() as conn:
       for table in conn.execute("SELECT name FROM sqlite_master WHERE type='table'").fetchall():
         conn.execute("DELETE FROM %s" % table)
 

my2to3/trace.py

 import __builtin__, imp, os, sqlite3, sys, types
-
+from contextlib import contextmanager
 from lib2to3.pgen2 import tokenize
 from lib2to3.refactor import get_fixers_from_package, RefactoringTool
 
 database = "traces.db"
+@contextmanager
+def connection():
+  conn = sqlite3.connect(database)
+  try:
+    with conn:
+      yield conn
+  finally:
+    conn.close()
 
 
 tracing_functions = []
 
-
 def create_table(table, *columns):
-  conn = sqlite3.connect(database)
-  with conn:
+  with connection() as conn:
     v = ', '.join(columns)
     conn.execute(
       "CREATE TABLE IF NOT EXISTS %s (%s, UNIQUE (%s))" % (table, v, v)
     )
-  conn.close()
 
   def insert_unique(*values):
-    conn = sqlite3.connect(database)
-    with conn:
+    with connection() as conn:
       try:
         conn.execute(
           'INSERT INTO %s VALUES (%s)' % (table, ', '.join('?' * len(values))),
@@ -29,7 +33,6 @@ def create_table(table, *columns):
       except sqlite3.IntegrityError as e:
         if not str(e).startswith('UNIQUE constraint failed:'):
           raise
-    conn.close()
   return insert_unique
 
 
@@ -46,10 +49,8 @@ def get_data(table, columns_to_select='*', conditions={}):
   )
   if conditions:
     query += " WHERE " + ' AND '.join(k + " = :" + k for k in conditions.keys())
-  conn = sqlite3.connect(database)
-  with conn:
+  with connection() as conn:
     return conn.execute(query, conditions).fetchall()
-  conn.close()
 
 
 def apply_fixers(string, name):