Python's .remove() Method Removes Unexpected Item in List

Question

I wrote this script:

soilMod = ['ptaaco']
n = 2

soilModSplit = [soilMod[i:i+n] for i in range(0, len(soilMod), n)] # This returns ['pt', 'aa', 'co']

alphaTest = soilModSplit # I want to maintain the original list built before I remove items below. This returns ['pt', 'aa', 'co'] as well

if 'pt' in soilModSplit:
      soilModSplit.remove('pt')
      print soilModList # This returns ['aa', 'co']
      print alphaTest # This also returns ['aa', 'co'] It's missing the original ['pt', 'aa', 'co'] and I didn't ask the script to remove it from this particular list.

For some reason, when I remove the item ('pt') from soilModSplit, it also removes the item from alphaTest. Is this the expected result? It seems like any variable built on the soilModSplit (in this case, alphaTest) is dependent on any action taken on the soilModSplit. Maybe I am doing something wrong? Is there a way to work around this?

Thanks, Mike

@JoeFrambach Although that fixes the problem, it doesn't answer the question — jamylak, Jun 10 '13 at 19:54
Joe Frambach. I searched around and didn't find that post. Maybe if I used the 'Clone' keyword. That post actually answers a few other questions I had, so thanks for providing that to me. — Mike, Jun 10 '13 at 20:02

score 2 · Accepted Answer · answered Jun 10 '13 at 19:45

2

alphaTest = soilModSplit

alphatest is just a another name for the same list binded to soilModSplit. Make a shallow copy:

alphaTest = list(soilModSplit )

answered Jun 10 '13 at 19:45

jamylak

128,818
30
231
230

Thanks jamylak. I did not realize that it didn't make a copy. Very good to know. I implemented that into my script and i am getting the result I need :) – Mike Jun 10 '13 at 19:48

score 1 · Answer 2 · answered Jun 10 '13 at 19:46

1

When you do alphaTest = soilModSplit, you are not creating a copy. You just have two names referencing the same list. If you want to save a copy, do alphaTest = list(soilModSplit).

answered Jun 10 '13 at 19:46

BrenBarn

242,874
37
412
384

Will `soilModSplit[:]` work in Python 3? – Alexei Sholik Jun 10 '13 at 19:47
Yes, either one will work. – BrenBarn Jun 10 '13 at 19:48

Python's .remove() Method Removes Unexpected Item in List

2 Answers2