How to create the strings sequence into specified line in edited text?

Here is the initial text.

test1
test2

Only two lines in the text.

I want to insert strings sequence into from 5th line into 16th line. I have tried it with below codes.

for i in range(1,12)  
    echo ".item".i.","
endfor  

1.the initial text.
2.to enter into command mode and input the codes

Two problems to be solved.
1.echo command output the first string .item1 before endfor.

for i in range(1,12)  
    echo ".item".i.","

2.How create the strings sequence into specified line:from 5th till 16th in edited text with vimscript?

The desired result is as below.

Almost done！
What i get is as below with the command :pu! =map(range(1,12), 'printf(''item%1d'', v:val)').

Both of them can't work.

:5pu! =map(range(1,12), 'printf(''item%1d'', v:val)')
:5,16pu! =map(range(1,12), 'printf(''item%1d'', v:val)')

The last issue for my desired format is when the cursor is on the 3th line ,how to create the desired output?