put

The put proc is used to add fields to point in the current stream.

...  | put(*field_assignments) | ...

Argument	Description	Required?
*field_assignments	list of field assignments to make to each point	No, default: None

A field assignment can be as simple as foo='bar' or can also be an assignment to a reducer such as foo=count().

add a count field

from flume import *

(
    emit(limit=5)
    | put(count=count())
    | keep('count'
    | write('stdio')
).execute()

The above would produce the output:

{"count": 1}
{"count": 2}
{"count": 3}
{"count": 4}
{"count": 5}