Python decimal range() step value

Question

Is there a way to step between 0 and 1 by 0.1? I thought I could do it like the following but it failed:

for i in range(0, 1, 0.1):
    print i

Instead, it says that the step argument cannot be zero, which it's not.

Thanks.

Answer 1

Why don't you increase the magnitude of i for the loop and then reduce it when you need it.

for i * 100 in range(0, 100, 10):
    print i / 100.0

Answer 2

The range() built-in function returns a sequence of integer values, I'm afraid, so you can't use it to do a decimal step.

I'd say just use a while loop:

i = 0.0
while i <= 1.0:
    print i
    i += 0.1

If you're curious, Python is converting your 0.1 to 0, which is why it's telling you the argument can't be zero.

Answer 3

Python's range() can only do integers, not floating point. In your specific case, you can use a list comprehension instead:

[x * 0.1 for x in range(0, 10)]

(Replace the call to range with that expression.)

For the more general case, you may want to write a custom function or generator.

Answer 4

And if you do this often, you might want to save the generated list r

r=map(lambda x: x/10.0,range(0,10))
for i in r:
    print i

Answer 5

Building on 'xrange([start], stop[, step])', you can define a generator that accepts and produces any type you choose (stick to types supporting + and <):

>>> def drange(start, stop, step):
...     r = start
...     while r < stop:
...      yield r
...      r += step
...      
>>> i0=drange(0.0, 1.0, 0.1)
>>> ["%g" % x for x in i0]
['0', '0.1', '0.2', '0.3', '0.4', '0.5', '0.6', '0.7', '0.8', '0.9', '1']
>>>

Answer 6

You can also use the numpy library (which isn't part of standard library but is relatively easy to obtain) which has the arange function:

>>> import numpy as np
>>> np.arange(0,1,0.1)
array([ 0. ,  0.1,  0.2,  0.3,  0.4,  0.5,  0.6,  0.7,  0.8,  0.9])

as well as the linspace function which lets you have control over what happens at the endpoint (non-trivial for floating point numbers when things won't always divide into the correct number of "slices"):

>>> np.linspace(0,1,11)
array([ 0. ,  0.1,  0.2,  0.3,  0.4,  0.5,  0.6,  0.7,  0.8,  0.9,  1. ])
>>> np.linspace(0,1,10,endpoint=False)
array([ 0. ,  0.1,  0.2,  0.3,  0.4,  0.5,  0.6,  0.7,  0.8,  0.9])

Answer 7

The Python Cookbook has a recipe for this: http://code.activestate.com/recipes/66472/

Be sure to check the comments; they include improved versions and discussion of errors (for example, gimel's solution may accumulate errors due to repeated addition of floating point numbers).

Answer 8

or you can use this function:

def frange(start,end,step):
 return map(lambda x: x*step, range(int(start*1./step),int(end*1./step)))