This example demonstrates how to wait for 10 seconds before accepting a call. Example Request 
from plivo import plivoxml

response = (plivoxml.ResponseElement()
            .add(plivoxml.WaitElement(None)
                 .set_length(10)).add(plivoxml.SpeakElement('Hello')))
print(response.to_string())
Response 
<Response>
    <Wait length="10" />
    <Speak>Hello</Speak>
</Response>