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.dynamicsgp as mod
conn = mod.connect("CompanyId=mycompanyId;user=myuser;password=mypassword;URL=http://{servername}:{port}/Dynamics/GPService")
cur = conn.cursor()
cmd = "SELECT * FROM sys_tablecolumns WHERE TableName = 'Customer'"
cur.execute(cmd)
rs = cur.fetchall()
for row in rs:
	print(row)