Strange Python output for counter loop

Question

import numpy as np
    from numpy.random import randn
    N = 100000
    counter = 0
    for i in randn(N):
        if i < 1 and i > -1:
            counter = counter + 1
    counter/N

The code resulted in an output of ZERO everytime.

I changed the 100000 to 100000.0 and it gave me the 68% but informed me the following:

anaconda/lib/python2.7/site-packages/ipykernel/main.py:5: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future"

Can you help me figure out what is happening?

That's because of [integer division](http://stackoverflow.com/questions/2958684/python-division). When you use a float, it works properly but that's not an appropriate input for randn. So either use Python 3's division (check the linked answer for importing that) or change the last line to `counter/float(N)`. — ayhan, Aug 31 '16 at 19:23
just a friendly suggestion, you could replace line n°7 with `counter += 1` — Daniel Kravetz Malabud, Aug 31 '16 at 19:24
You're not returning anything.Your indenting is strange (everything after the first line is indented one time too many), which may be causing a problem. — Vivian, Aug 31 '16 at 19:25
About *VisibleDeprecationWarning* - it shows up because the function *numpy.random.randn* does not like to receive a float parameter. — turdus-merula, Aug 31 '16 at 19:29

Jakube · Accepted Answer · 2016-08-31T19:29:22.110

You are performing an integer division. Integer division means, that it will round down the result of the division, like

>>> print(99 / 100)
0

You can perform a "normal" division, by converting one (or both) of the operands to a float.

float(counter) / float(N)

The other effect that you see (the VisibleDeprecationWarning) results from N being an float in this case. The function randn takes an integer as parameter, not a float. See numpy.random.randn. An older version of numpy allowed using a float, but now it is deprecated. This means, that it will still work, but isn't good practice anymore.

Thank you, user :) – Фанки Джаз Aug 31 '16 at 19:27 — Фанки Джаз, Aug 31 '16 at 19:27

score 1 · Answer 2 · answered Aug 31 '16 at 19:27

First of all, I'd recommend you indent your code properly so users can run it directly to diagnose your bug. Anyway, given your snippet properly formatted:

import numpy as np
from numpy.random import randn

N = 100000
counter = 0
for i in randn(N):
    if i < 1 and i > -1:
        counter = counter + 1

print(counter, N, counter / N)

Problem happens when you do counter/N using python 2.x, if that's the case you need to cast to float explicitely float(counter)/float(N). If you just used python 3.x, that float cast would be done automatically, so you wouldn't need to do it explicitely

Strange Python output for counter loop

2 Answers2