error: an integer is required

[madigreece at yahoo.gr]

I execute my code in linux environment.
My code is:

from os import *

def insert_text_file(self, strng):
     t=open("elements_file.txt", "a")
     t.write(strng)
     t.close()

I'm getting this error:

<type 'exception.TypeError'>: an integer is required

Where is the mistake?
Help me, please!!