Python for loop with small steps

Question

How can I make an for loop in python with steps of 0.01?

I tried this but it doesn't work:

 for X0 in range (-0.02, 0.02, 0.01):
     for Y0 in range (-0.06, 0.09, 0.01):

it says TypeError: range() integer end argument expected, got float.

See this question if you want to code a `range` function that accepts floats or if you want to use numpy: http://stackoverflow.com/questions/477486/python-decimal-range-step-value — Nicolas, Apr 25 '13 at 16:44
This question has been asked and answered before. http://stackoverflow.com/questions/477486/python-decimal-range-step-value — AlexLordThorsen, Apr 25 '13 at 16:46

score 8 · Answer 1 · answered Apr 25 '13 at 16:43

8

[x * 0.01 for x in xrange(10)]

will produce

[0.0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09]

answered Apr 25 '13 at 16:43

mjallday

9,796
9
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71

How do I do this with a double loop? – Steven Apr 25 '13 at 16:44
for X0 in range ([X0 * 0.01 for x in xrange(-2,2)]): – Steven Apr 25 '13 at 16:46
Just replace "range(...)" by the above list (or other iterator). – tiago Apr 25 '13 at 16:46
+1 but im recommend using range, not xrange. range in Python 3.x is xrange from Python 2.x. – ndpu Apr 25 '13 at 16:49
@ndpu As you said, `xrange()` in py2 is the same as `range()` in py3, so he's using py3's `range()`... You're recommending him to use what he's already using. – Apr 25 '13 at 16:57
@ndpu - 2to3 will automatically change xrange->range if you migrate code. you're correct that range should be used in python3 however. – mjallday Apr 25 '13 at 16:57
edit: nevermind, fixed it.. thanks for your help. – Steven Apr 25 '13 at 17:15

tiago · Answer 2 · 2013-04-25T16:49:08.790

The python range only takes integers as the error message indicates. If you want to use float steps, you can either use numpy's arange or just divide a integer range:

>>> import numpy as np
>>> print np.arange(-0.02, 0.02, 0.01)
array([-0.02, -0.01,  0.  ,  0.01])

in your example:

for X0 in np.arange(-0.02, 0.02, 0.01):
    for Y0 in np.arange(-0.06, 0.09, 0.01):

or:

>>> print [a/0.01 - 0.02 for a in range(4)]
[-0.02, -0.01, 0.0, 0.009999999999999998]

score 5 · Answer 3 · answered Apr 25 '13 at 16:54

5

If you don't want to use a library:

def float_range(a,b,c):
    while a < b:
        yield a
        a += c
for X0 in float_range (-0.02, 0.02, 0.01):
    for Y0 in float_range (-0.06, 0.09, 0.01): 
        print X0, Y0

answered Apr 25 '13 at 16:54

Hal Canary

2,154
17
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Python for loop with small steps

3 Answers3