def myrange(stop_at, start_at=0, step=1):
 val = start_at
 while val < stop_at:
  yield val
  val+=step

for f in myrange(1,step=0.1):
 print(f)

>>> def g(start, stop, step):
...     while stop <= start:
...         yield start
...         start += step
>>> list(g(0.4, 0., -0.1))
0: [0.4,
 0.30000000000000004,
 0.20000000000000004,
 0.10000000000000003,
 2.7755575615628914e-17]
>>> list(range(4, 0, -1))
1: [4, 3, 2, 1]
>>>