List Comprehension (Python)

Question

Q. Write a function
remove(data, value)
that returns a new list that contains the same elements as the list data except for those that equal value. Use a list comprehension. Your function should remove all items equal to value. For example, remove([3, 1, 5, 3, 9], 3) should return the list [1, 5, 9].

Down below is what I worked on, but it returns None.

def remove (data,value):
    ans = [ data.remove(value) for ele in data if value == ele ]
    return ans

assert(remove([3,1,5,3,9], 1) ==[3,5,3,9])

These should work for this function. Please let me know what should I do ??

Why do you think it returns `[None]`? What does `data.remove()` return? What's the point of modifying `data` if you're returning `ans`? — wjandrea, Aug 27 '20 at 02:40
Please [edit] the question to have a descriptive title. BTW welcome to SO! Check out the [tour] and [ask]. It would help if you provided the actual output in the question itself. See [mre] for reference. — wjandrea, Aug 27 '20 at 02:42
Does this answer your question? [Remove all occurrences of a value from a list?](https://stackoverflow.com/questions/1157106/remove-all-occurrences-of-a-value-from-a-list) Specifically [this answer](https://stackoverflow.com/a/1157132/4518341) — wjandrea, Aug 27 '20 at 02:45

score 0 · Answer 1 · edited Aug 27 '20 at 02:51

0

you cannot remove elements in a list while you're iterating over it. create a new list and keep all elements except the ones that match ele.

def remove(data, value):
    ans = [ele for ele in data if value != ele]
    return ans

edited Aug 27 '20 at 02:51

wjandrea

28,235
9
60
81

answered Aug 27 '20 at 02:47

Taha Rind

1

1

*"you cannot remove elements in a list while you're iterating over it"* - You can actually, but it might cause unexpected results. – wjandrea Aug 27 '20 at 02:50
BTW welcome to SO! Check out the [tour], and [answer] if you want advice. – wjandrea Aug 27 '20 at 02:50

score 0 · Answer 2 · answered Aug 27 '20 at 13:31

This is a duplicate of Remove all occurrences of a value from a list? however, I don't think your case of the issue is well-explained.

There are a few clear issues which are seen in the comments, but not clearly Answering the Question.

.remove() method of lists will remove the first instance of its argument and then return None
you both change the original list and create a new list, while you would be better served by only doing one as-detailed by numerous answers in the duplicate question!

score -1 · Answer 3 · edited Aug 27 '20 at 02:47

-1

def remove(data, value):
   return [i for i in data if i != value]

This will iterate over everything properly.

edited Aug 27 '20 at 02:47

wjandrea

28,235
9
60
81

answered Aug 27 '20 at 02:41

neuops

342
3
16

List Comprehension (Python)

3 Answers3