make Session a context manager

bindings/python/example_scripts/simple_test.py

@@ -7,7 +7,7 @@ from gnucash import Session, Account, Transaction, Split, GncNumeric
 
 FILE_1 = "/tmp/example.gnucash"
 
-session = Session("xml://%s" % FILE_1, is_new=True)
+with Session("xml://%s" % FILE_1, is_new=True) as session:
 
     book = session.book
     root_acct = Account(book)
@@ -81,7 +81,3 @@ split4.SetValue(num2.neg())
 
     trans1.CommitEdit()
     trans2.CommitEdit()
-
-session.save()
-session.end()
-session.destroy()

bindings/python/gnucash_core.py

@@ -117,6 +117,15 @@ class Session(GnuCashCoreClass):
                 self.destroy()
                 raise
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback):
+        # Roll back changes on exception by not calling save. Only works for XMl backend.
+        if not exc_type:
+            self.save()
+        self.end()
+
     def raise_backend_errors(self, called_function="qof_session function"):
         """Raises a GnuCashBackendException if there are outstanding
         QOF_BACKEND errors.