Botocore Events#

Botocore will emit events during various parts of its execution. Users of the library can register handlers (callables) for these events, such that whenever an event is emitted, all registered handlers for the event will be called. This allows you to customize and extend the behavior of botocore without having to modify the internals. This document covers this event system in detail.

Session Events#

The main interface for events is through the botocore.session.Session class. The Session object allows you to register and unregister handlers to events.

Event Types#

The list below shows all of the events emitted by botocore. In some cases, the events are listed as event-name.<service-id>.<operations>, in which <service-id> and <operation> are replaced with a specific service identifier operation, for example event-name.s3.ListObjects.

  • 'before-send.<service-id>.<operation>'


Full Event Name:



This event is emitted when the operation has been fully serialized, signed, and is ready to be sent across the wire. This event allows the finalized request to be inspected and allows a response to be returned that fufills the request. If no response is returned botocore will fulfill the request as normal.

Keyword Arguments Emitted:
type request:


param params:

An object representing the properties of an HTTP request.

Expected Return Value:

None or an instance of AWSResponse

Event Emission#

When an event is emitted, the handlers are invoked in the order that they were registered.

Service ID#

To get the service id from a service client use the following:

import botocore
import botocore.session

session = botocore.session.Session()
client = session.create_client('elbv2')
service_event_name = client.meta.service_model.service_id.hyphenize()