How to resolve pyaws Missing parameter problem?

I am using pyAWS wrapper for Amazon Web services. I want to show amazon sea开发者_高级运维rch results on my web sites. For search I am using following codes.

from pyaws import ecs
ecs.setLicenseKey('Your-AWS-License-Key')
books = ecs.ItemSearch('python', SearchIndex='Books')

But it gives an error: u'ingParameter'