Passing by reference? An copied array question...

[pholvey]

Hi guys. I'm brand new to this forum, so if I'm messing up by starting my own thread, I'm sorry. But this array problem I'm running into has got me hitting a brick wall.

I'm in Python, and I've imported Numeric. And I'm on Fedora.

I'm trying to make a copy of a 3x3 array, modify the copy, then subtract the original array from the copy to see what's left. But every time I change the copy, the original changes too, so the final difference between the two 3x3 arrays is 0 in every element.

I looked around online and it looks like Python passes by reference, right? So whatever I do to the "copied" array is passed back to the original. I saw somewhere that

..newarray = oldarray[:]..

was supposed to make a physical copy and avoid the problem, but it didn't work for me.

Here's what I'm running:

..sitewater=masterwater[:]
print masterwater
print sitewater
sitewater[2,0]=3
print sitewater
print masterwater..

and the output is:

..[[  2.157016   0.931734  18.799198]
 [  1.484143   2.309928  18.915375]
 [  1.283086   1.359119  18.840746]]
[[  2.157016   0.931734  18.799198]
 [  1.484143   2.309928  18.915375]
 [  1.283086   1.359119  18.840746]]
[[  2.157016   0.931734  18.799198]
 [  1.484143   2.309928  18.915375]
 [  3.         1.359119  18.840746]]
[[  2.157016   0.931734  18.799198]
 [  1.484143   2.309928  18.915375]
 [  3.         1.359119  18.840746]]..

Any ideas? Any advice on how to better ask questions would be appreciated too!

Thanks,
pholvey

[jlm699]

import copy
newObj = copy.deepcopy(oldObj)
 

this will prevent the "shallow copy" problem of which you speak.

[pholvey]

Looks like it worked just fine. Thanks guys!

pholvey

import copy
newObj = copy.deepcopy(oldObj)
 

this will prevent the "shallow copy" problem of which you speak.