Need to use range with decimals

[KameronG]

Hello,

I need to write a program that asks for values from a user and then use the values in a formula. One thing I need to do is ask the user if they want a range, list, or single value for one of the parameters, but I can't figure out how to do this. I don't think I'm allowed to use numpy for this. Here is my code:

import math

h = float(input("What is the value of H0 (in km/s/Mpc)?"))
z = float(input("What is the value of the redshift?")
j = float(input("what is the value of the matter density parameter?"))
cs = input("Do you want a flat or open cosmology (1 = flat, 0 = open)?")
ran = input("Do you want a range of readshifts (min, max, increment), or a list (type range, list, o$

if ran == "range":
    i = float(input("What is the minimum of the range you desire (enter min z value)?"))
    k = float(input("What is the maximum of the range you desire (enter max z value)?"))
    u = float(input("By what increment do you want z to be calculated (enter increment size)?"))
    for z in range(i, k, u):
        z = z + u

There's more after that, but I don't want to post my entire code for this issue unless I have to.
So, the range gives me SOMETHING if I give it only integers, but it only gives me one value and I don't know why. For example, if I use (1, 3, 1), it only gives one value instead of 3. Beyond this, using integers only makes the range pointless as redshifts aren't often integers.If anyone knows a way this can be done, I greatly appreciate it. Thank you.