looping over the rows in a table

Hi, this is slightly offtopic, but is based on Postgres:

I have a table with 10M rows and I have a Python script using psycopg
that needs to look at each row of the table. My current strategy is
to do in the Python script

cursor.execute("select acol from atable")
while True:
    ret = cursor.fetchone()
    if not ret: break

However if I understand correctly Postgres will basically try and
return *all* the rows of the table as the result set, thus taking a
long time and probably running out of memory.

Is there a way I can modify the SQL or do something on the Postgres
side, so that I can loop over all the rows in the table?

Thanks,

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Rajarshi Guha  <rguha@indiana.edu>
GPG Fingerprint: 0CCA 8EE2 2EEB 25E2 AB04  06F7 1BB9 E634 9B87 56EE
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A bug in the hand is better than one as yet undetected.