CODEWITHSUNDEEP
pythonpython-3.x
Mr Nielsen
Mr Nielsen

Reputation: 11

How to create a new list, by appending a value in a certain position on and old list

I am trying to make a new list, which is a replica of an other list. This new list I want to modify by changing values at specific positions.

I found this question, and the most upvoted answer can make a new list and add on to the old list. This is a good start, but I want to decide where the additions are done (in his version, it just adds it on to the end of the list)

What he has: 

myList = [10,20,30] 

yourList = myList + [40]

print("your list: " + yourList)

your list: [10,20,30,40]

In this instance, I would want to be able to change where the 40 in your list goes ie

your list: [10,40,20,30]

I'm unsure how I would go about doing that. Thanks! (Pretty new here sorry if I'm not clear)

Upvotes: 1

Views: 1628

Answers (3)

juancarlos
juancarlos

Reputation: 631

you can copy your list and insert the value in the new list something like this:

my_list = [1,2,3,4,5,6]
my_2_list = my_list.copy()

then i wnat to insert a vlue at position 3 i can do

my_2_list.insert(3, value)

Upvotes: 0

ShadowRanger
ShadowRanger

Reputation: 155418

Use slicing to split the original list apart at the desired index, then put it back together again.

For example:

insert_at = 1

myList = [10,20,30] 

# Uses PEP 448 unpacking generalizations to avoid excess temporary `list`s
yourList = [*myList[:insert_at], 40, *my_list[insert_at:]]

# Or via concatenation (involves an extra temporary)
yourList = myList[:insert_at] + [40] + my_list[insert_at:]

print("your list: " + yourList)

Alternatively, if you don't need a one-liner, copy the list, then call insert on the copy:

yourList = myList[:]  # myList.copy() also works on Python 3
yourList.insert(insert_at, 40)

Upvotes: 1

rdas
rdas

Reputation: 21275

To keep the same list:

Use the insert method of the list class

myList.insert(1, 40)

insert(index, element) inserts the element into the list at the position index - shifting the remaining elements rightward as required.

To make a new list:

new_list = myList.copy()
new_list.insert(1, 40)

Upvotes: 0

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