You can get the same functionality of Python's count
using in-range
with an infinite end
value:
(define (count start step)
(in-range start +inf.0 step))
For example:
(define s (count 2.5 0.5))
(stream-ref s 0)
=> 2.5
(stream-ref s 1)
=> 3.0
(stream-ref s 2)
=> 3.5
(stream-ref s 3)
=> 4.0