use native pg 'copy' to or from...

sa_pgsql_copy_expert.py

def pgsql_copy(session,tablename,string_buffer,direction="from"):
    """
    Args:
        session:  a SA session that with a started transaction.
        tablename:  the table to write into
        string_buffer:  handle to a filelike, with seek set to 0
        direction: from|to, which way it should go.
        sele
    Returns:
        True on success, raises on errror
    
    Note:  
        1. This isn't really containable in a session, given pgcopy.
        2. If you want to use a selectable in 'to' copying,
           wrap it in parens as shown in example below.  
        3. 'from' means from string_buffer to db
           'to' is from db to string_buffer
    
    example:
    
    ## hack:  selectables for 'to' need to be wrapped in parens...
    # psql_copy(session, "(select 1)", buf, 'to') # does....
    # > COPY (select 1) TO STDOUT WITH DELIMITER E'\t';
    """
    if direction not in ('from','to'): 
        raise ValueError("direction must be one of: from|to")
    
    if direction == 'from':
        SQL = '''COPY %(tablename)s FROM STDIN USING DELIMITERS E'\t' ''' \
            % (dict(tablename=tablename))
    else:
        SQL = '''COPY %(tablename)s TO STDOUT WITH DELIMITER E'\t';''' \
            % (dict(tablename=tablename))
    connection = session.connection()
    # We need the raw psycopg-cursor, hidden deep within SA's abstractions.
    cursor = connection.connection.cursor().cursor
    cursor.copy_expert(SQL, string_buffer)
    return True