SQLite: Command-line vs Python: Distinct command acts differently

I need help understanding why a sql command works on the command line however it doesn't work when executed from python 2.7.

The goal is to "squeeze" out NULLs from a column if there is only 1 unique real value in that column. For example:

In SQL:

create table foo (FirstName char(20), LastName char(20));
insert into foo values ('Joe', 'Smith');
insert into foo values ('Susan', NULL);
insert into foo values ('Shirley', 'Smith');
insert into foo values ('Kevin', NULL);

Since there is only one last name, I want to replace the NULLs with Smith. This works on the command line.

UPDATE foo
SET LastName = 
    ( CASE
         WHEN ((select count(distinct LastName) from foo) = 1)  THEN (SELECT distinct LastName from foo)
         ELSE LastName
      END
    );

In Python:

con = lite.connect('test.db')
names = (
    ('Joe', 'Smith'),
    ('Susan', None),
    ('Shirley', 'Smith'),
    ('Kevin', None),
)

squeezecmd = '''UPDATE foo SET LastName = (CASE
    WHEN ((select count(distinct LastName) from foo) = 1)
    THEN (SELECT distinct LastName from foo) ELSE LastName END);'''


with con:
    cur = con.cursor()
    cur.execute("CREATE TABLE foo(FirstName TEXT, LastName TEXT)")
    cur.executemany("INSERT INTO foo VALUES(?, ?)", names)

    cur.execute(squeezecmd)
    cur.execute("SELECT * FROM foo")
    rows = cur.fetchall()

    for row in rows:
        print row

This results in replacing every value in LastName with None (or NULL). I think it's because distinct(LastName) results in a list instead of a single value like on the command line but I'm not sure.

Any ideas?

EDIT:

So SELECT distinct LastName from foo results in 1 answer in SQL but 2 answers in Python. SQL responds with "Smith" while Python gives [None, u"Smith"] . Any way to make the python distinct ignore the NULLs?