Encountered an error

I am trying to insert a new record into my "prototypedb" database. This
here below is the section of my code that I am using to access and work on
my database.

What I am trying to do here is enter one record (three values) in three
columns name, code and type. Then create a new column and then add one
value to the new column for the aforementioned already entered record.

cur = conn.cursor()

#Enter the three value basic record
cur.execute("""INSERT INTO inventory (name, code, type)
VALUES (%s, %s, %s);""",
[self.entry_product_name.get_text(), self.new_product_code.get_text(),
self.new_product_type.get_text()])

#Take out list of Text Entry boxes
#self.quantity_list is a list of two value tuples each of which
holds a reference to a text box in my GUI
for x in self.quantity_list:
if x[0].get_text() !="" and x[1].get_text() != "":
#First make the appropriate column
cur.execute("""ALTER TABLE inventory
ADD %s integer DEFAULT NULL;""",
[x[0].get_text()])
#Then give that column the appropriate value for the
current record
cur.execute("""UPDATE inventory
SET %s = %s
WHERE name = %s;""", [x[0].get_text(),
x[1].get_text(), self.entry_product_name.get_text()])
else:
continue;

conn.commit()
cur.close()
conn.close()

But Alas! There is an Error!

Traceback (most recent call last):
File "C:\Python34\prototype_husk.py", line 134, in submit_data
ADD %s integer DEFAULT NULL;""", [x[0].get_text()])
psycopg2.ProgrammingError: syntax error at or near "'26.2 LTRS'"
LINE 2: ADD '26.2 LTRS' integer DEFAULT ...
^

I have attached herein a screenshot of the values entered. So the error can
make more sense.