Second argument of three mandatory

Question

I have a function that mimics range(). I am stuck at one point. I need to be able to make the first (x) and third (step) arguments optional, but the middle argument (y) mandat

Answer 1

You have to use sentinel values:

def float_range(value, end=None, step=1.0):
    if end is None:
        start, end = 0.0, value
    else:
        start = value

    if start < end:
        while start < end:
            yield start
            start += step
    else:
        while start > end:
            yield start
            start += step

for n in float_range(0.5, 2.5, 0.5):
    print(n)
#  0.5
#  1.0
#  1.5
#  2.0

print(list(float_range(3.5, 0, -1)))
#  [3.5, 2.5, 1.5, 0.5]

for n in float_range(0.0, 3.0):
    print(n)
#  0.0
#  1.0
#  2.0

for n in float_range(3.0):
    print(n)
#  0.0
#  1.0
#  2.0

By the way, numpy implements arange which is essentially what you are trying to reinvent, but it isn't a generator (it returns a numpy array)

import numpy

print(numpy.arange(0, 3, 0.5))
# [0.  0.5 1.  1.5 2.  2.5]