Replace elements in list - with a nested list containing said elements (python3)

Question

I am trying to replace elements in a list with a list containig said elements, for example:

list = ['cow','orange','apple','mango']
to_replace = 'orange', 'apple'
replace_with = ['banana','cream']

Desired output:

['cow', ['banana', 'cream'], 'mango']

I've read the answers in this question 1 and tried the function mentioned there:

def replace_item(list, to_replace, replace_with):
    for n,i in enumerate(list):
      if i== to_replace:
         list[n]=replace_with
    return list

but it does nothing. I also tried a basic equality functions:

list[1:3] = ['banana','cream']

However neither work. Is there a function to accomplish this? In my actual problem which is a loop, list[1:3] is an iterator, i.e. list[i:i+2]. I am not sure if this makes a difference. The items to be replaced will always be sequential.

Sriram A. · Accepted Answer · 2021-01-12 04:37:30Z

2

Try this:

List[1:3] = [["banana", "cream"]]

The reason this isnt working is because when you are writing: List[1:3] = ["banana", "cream"] you are replacing a list with a list. In other words you are changing ["orange", "apple"] to ["banana", "cream"].

When doing this: List[1:3] = [["banana", "cream"]] you replace a list with a list in a list, replacing ["orange", "apple"] with [["banana","cream"]], thereby replacing "orange", "apple" with ["banana", "cream"]

answered Jan 12, 2021 at 4:37

Sriram A.

786 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Synthaze · Accepted Answer · 2021-01-12 04:33:43Z

def replace_item(lst, to_replace, replace_with):
    for n,i in enumerate(lst):
      if i in to_replace and lst[n+1] in to_replace:
         lst[n]=replace_with
         lst[n+1] = ""
    return [item for item in lst if item]

lst = ['cow','orange','apple','mango']
to_replace = 'orange', 'apple'
replace_with = ['banana','cream']

print (replace_item(lst, to_replace, replace_with))

Output:

['cow', ['banana', 'cream'], 'mango']

First, don't call your var the same name as object type. That is a bad idea that can lead to code confusion/bugs etc.

In your function, the problem was essentially that the == operator between a string (i) and a list (lst) will never say True regardless the rest. Plus, the content in string in the list is not the same as in your string. So you use in instead of ==.

After this, if you don't want to have a duplicate and wish to replace adjacent 'orange', 'apple' by a single ['banana','cream'], you need to check lst[n+1] when iterating.

Then you replace lst[n], set lst[n+1] to nothing and return a list purged from nothing elements using list comprehension.

thanks very much, for some reason in my loop this gives me "index out of range" error, not sure where the error is from but the solution above worked

Collectives™ on Stack Overflow

Replace elements in list - with a nested list containing said elements (python3)

2 Answers 2

Comments

2 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Linked

Related