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.sapbusinessobjectsbi as mod
conn = mod.connect("User=MyUser;Password=MyPassword;Url=http://myserver:6405/biprws;")
cur = conn.cursor()
cmd = "SELECT * FROM sys_tablecolumns WHERE TableName = 'MyCustomReport'"
cur.execute(cmd)
rs = cur.fetchall()
for row in rs:
	print(row)