Python: Copying a list and removing an element at the same time

Question

I am new to python and am trying to create a copy of a list without a certain element. This is how I am doing it at the moment:

oldList[1,23,4,3,5,345,4]
newList = oldList[:]
del newList[3]
doSomthingToList(newList)

I was wondering if there is a better more eloquent way to do this, instead of copying the list and then deleting the element in two lines?

Is the element excluded because of its index (i.e. "all elements except the third") or because of something more complex (i.e. "all elements except those that are larger than 200")? — Stefano Sanfilippo, Feb 01 '14 at 14:39

falsetru · Answer 1 · 2014-02-01T14:46:31.487

2

Using list comprehension:

>>> oldList = [1,23,4,3,5,345,4]
>>> newList = [x for i, x in enumerate(oldList) if i != 3] # by index
>>> newList
[1, 23, 4, 5, 345, 4]

>>> newList = [x for x in oldList if x != 4] # by value
>>> newList
[1, 23, 3, 5, 345]

edited Feb 01 '14 at 14:46

answered Feb 01 '14 at 14:38

falsetru

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score 2 · Accepted Answer · answered Feb 01 '14 at 14:40

2

oldList[1,23,4,3,5,345,4]
newList = oldlist[:3] + oldList[4:]
doSomthingToList(newList)

answered Feb 01 '14 at 14:40

Eugene P.

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score 0 · Answer 3 · answered Feb 01 '14 at 14:41

0

Try this with 'slicing':

>>> oldList = [1, 2, 3, 4, 5]
>>> newList = oldList[:2] + [oldList[3:]
>>> newList
[1, 2, 4, 5]

answered Feb 01 '14 at 14:41

Kevin

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score 0 · Answer 4 · answered Feb 01 '14 at 15:03

Consider using the built-in function filter

oldList = [1, 2, 3, 4, 5]
newList = filter(lambda number: number != 3, oldList)

# newList == [1,2,4,5]

filter's arguments are function, iterable. It applies the function you give it to every element of the iterable and returns a list of the elements that the function returns True on.

Python: Copying a list and removing an element at the same time

4 Answers4