plpython/python string formatting

[Ted Toth <txtoth@xxxxxxxxx>]

I've just started playing with plpython but ran into a issue when I
was trying to use standard python string formatting to generate a SQL
string for example:
s = "EXECUTE format('CREATE INDEX %s ON %s USING (column_name)' %
(index_name, table_name))"

but plpython then tried to run the EXECUTE instead of just setting
variable 's'. Why does this happen?

Ted