How does iteration work in function

Question

here's my problem. Sorry for the previous post which was not clear at all.

so here's an example:

import numpy as np

x=np.arange(1,100,1)
y=z=x*0

def func(h,g):
    for i in range(1,50):
        h[i]=i+1
        g[i]=i*2

func(z,y)
print z-y

In this example z and y give the same answer, but why is that so? In the function it is not supposed to give the same answer?

possible duplicate of Iterator (iter()) function in Python

PW Kad
– PW Kad

2013-08-13 16:53:56 +00:00
Commented Aug 13, 2013 at 16:53 — PW Kad
– PW Kad, Commented Aug 13, 2013 at 16:53
@OP : You could also do this with np.zeros(...).

Sukrit Kalra
– Sukrit Kalra

2013-08-13 16:57:40 +00:00
Commented Aug 13, 2013 at 16:57 — Sukrit Kalra
– Sukrit Kalra, Commented Aug 13, 2013 at 16:57
@PeterDeGlopper Y I'm not confused about that :)

keyser
– keyser

2013-08-13 17:00:41 +00:00
Commented Aug 13, 2013 at 17:00 — keyser
– keyser, Commented Aug 13, 2013 at 17:00

Peter DeGlopper · Accepted Answer · 2013-08-13 16:54:42Z

4

You're setting y and z to both point to the same object. This line:

y=z=x*0

creates one new object, x*0, then sets both y and z to refer to it. Thus, h and g in your function are the same object, and the updates overwrite each other.

If you want to have two independent objects, create them independently:

y=x*0
z=x*0

answered Aug 13, 2013 at 16:54

Peter DeGlopper

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2 Comments

Vermz Over a year ago

Thank you! i thought the y=z=x*0 was just a way to reduce the number of lines!

Peter DeGlopper Over a year ago

Nope. It literally sets y to the return value of z=x*0, which is z.

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