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.informix as mod
conn = mod.connect("Server=10.0.1.2;Port=50000;User=admin;Password=admin;Database=test")
cur = conn.cursor()
cmd = "SELECT * FROM sys_tablecolumns WHERE TableName = '[informix].Books'"
cur.execute(cmd)
rs = cur.fetchall()
for row in rs:
	print(row)