替换列表中的元素 - 使用包含所述元素的嵌套列表（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, ie list[i:i+2] . I am not sure if this makes a difference. The items to be replaced will always be sequential.

Answer 1

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"]

Answer 2

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.