numpy.arange divide by zero error

Question

I have used numpy's arange function to make the following range:

a = n.arange(0,5,1/2)

This variable works fine by itself, but when I try putting it anywhere in my script I get an error that says

ZeroDivisionError: division by zero

Answer 1

First, your step evaluates to zero (on python 2.x that is). Second, you may want to check np.linspace if you want to use a non-integer step.

Docstring:
arange([start,] stop[, step,], dtype=None)

Return evenly spaced values within a given interval.

[...]

When using a non-integer step, such as 0.1, the results will often not
be consistent.  It is better to use ``linspace`` for these cases.

---

In [1]: import numpy as np

In [2]: 1/2
Out[2]: 0

In [3]: 1/2.
Out[3]: 0.5

In [4]: np.arange(0, 5, 1/2.)  # use a float
Out[4]: array([ 0. ,  0.5,  1. ,  1.5,  2. ,  2.5,  3. ,  3.5,  4. ,  4.5])

Answer 2

If you're not using a newer version of python (3.1 or later I think) the expression 1/2 evaluates to zero, since it's assuming integer division.

You can fix this by replacing 1/2 with 1./2 or 0.5, or put from __future__ import division at the top of your script.