plpython integer types

Hi everibody,
a plpython function i'm writing fail with a strange ( to me ) message error:

.....
plan=ply.prepare("intert into text,text1,integer1,text"
values($1,$2,$3,$4)",["text","text","integer","text"])
ply.execute(plan,[var1,var2,var3,var4])
.....


The backend raise an errore saying:
    ERROR: type integer does not exist...

I can't understand this....
How can i solve this problem, or, say, how can I cast python variables?