Say I want to create a list using list comprehension like:

l = [100., 50., 25., 12.5, ..., a_n]

…i.e., start with some number and generate the n "halves" from that in the same list. I might either be missing some straightforward pythonic way of doing that, or I'll simply have to rely on a good ol' for-loop. Can this be done? Thanks.

How about this?

start = 2500.0
n = 50
halves = [start / 2.0**i for i in range(n)]

equal to this:

[start * 2.0**(-i) for i in range(n)]

probably less efficient in contrast to @DeepSpace's answer but a one-liner