The available columns for any given table are fetched from a system table called "sys_tablecolumns". A specific table name is provided in the WHERE criteria to restrict the table from which the column information is fetched:

import cdata.greenplum as mod
conn = mod.connect("User=user;Password=admin;Database=dbname;Server=127.0.0.1;Port=5432")
cur = conn.cursor()
cmd = "SELECT * FROM sys_tablecolumns WHERE TableName = '\"template1\".\"public\".Orders'"
cur.execute(cmd)
rs = cur.fetchall()
for row in rs:
	print(row)