Why the comment can't be set at the second line instead of first line?

Question

I want to add some comment lines when to edit python file:

vim  .vimrc
autocmd BufNewFile *.py exec ":call SetTitle_py()"
func SetTitle_py()
        call append(line("."),   "#!/usr/bin/env python3" )
        call append(line(".")+1, "# -*- coding:utf-8 -*- ")
endfunc

The title is set at the second line when to edit a py file with vim test.py ,instead of the first line?

Answer 1

First, you should :help append() a list instead of calling append() several times and keeping track of the current line and all:

let boilerplate = [
    \ "#!/usr/bin/env python3",
    \ "# -*- coding:utf-8 -*- "
    \]
call append(line("."), boilerplate)

Second, append() adds lines after the given line. Since you are on line 1, line(".") returns 1 and the text ends up on line 2, as expected. If you want the text to appear on line 1, you will have to do:

let boilerplate = [
    \ "#!/usr/bin/env python3",
    \ "# -*- coding:utf-8 -*- "
    \]
call append(0, boilerplate)

Third, :help setline() might be a more intuitive alternative:

let boilerplate = [
    \ "#!/usr/bin/env python3",
    \ "# -*- coding:utf-8 -*- "
    \]
call setline(1, boilerplate)

Answer 2

I came up with a solution that coexists with the XDG file template mechanism.

Part 1: create a file template containing the shebang etc.

File ~/Templates/python.py:

#!/usr/bin/env python3
# -*- coding:utf-8 -*- 
"""
"""

Part 2: read from this file

In my vimrc:

autocmd BufNewFile *.py 0r ~/Templates/python.py

This will read the template file when creating a new file. Added benefit is that it allows me to create a new file from template in one of these new fashioned graphical file manager programs, e.g. Right click -> New Document -> python

I extended this for a number of other languages and find it scales well. Each language takes up one dedicated file template and one line of vimrc.