Python, SQL: How to update multiple rows and columns in a single trip around the database?

Hello StackEx community. I am implementing a relational database using SQLite interfaced with Python. My table consists of 5 attributes with around a million tuples. To avoid large number of database queries, I wish to execute a single query that updates 2 attributes of multiple tuples. These updated values depend on the tuples' Primary Key value and so, are different for each tuple.

I am trying something like the following in Python 2.7:

stmt= 'UPDATE Users SET Userid (?,?), Neighbours (?,?) WHERE Username IN (?,?)'
cursor.execute(stmt, [(_id1, _Ngbr1, _name1), (_id2, _Ngbr2, _name2)])

In other words, I am trying to update the rows that have Primary Keys _name1 and _name2 by substituting the Neighbours and Userid columns with corresponding values. The execution of the two statements returns the following error:

OperationalError: near "(": syntax error

I am reluctant to use executemany() because I want to reduce the number of trips across the database. I am struggling with this issue for a couple of hours now but couldn't figure out either the error or an alternate on the web. Please help.

Thanks in advance.