Question

I’m trying to figure out what the following line does exactly – specifically the %%s part?

cursor.execute('INSERT INTO mastertickets (%s, %s) VALUES (%%s, %%s)'%sourcedest, (self.tkt.id, n)) 

Any good mini-tutorial about string formatting and inserting variables into strings with Python?

Answer 1

The %% becomes a single %. This code is essentially doing two levels of string formatting. First the %sourcedest is executed to turn your code essentially into:

cursor.execute('INSERT INTO mastertickets (BLAH, FOO) VALUES (%s, %s)', (self.tkt.id, n)) 

then the db layer applies the parameters to the slots that are left.

The double-% is needed to get the db’s slots passed through the first string formatting operation safely.