I was wondering if there was any key mapping in Vim to allow me to indent certain lines of code (whether those lines have been selected in visual mode, or n lines above/below current cursor position).

So basically something that converts the following

def my_fun(x, y):
    return x + y

to

#def my_fun(x, y):
#    return x + y

I am okay with using either # or """ for commenting out the relevant lines. Ideally, I would also like the same keymapping to uncomment the lines if the given lines have been commented out.

Step 1: Go to the the first column of the first line you want to comment.

Step 2: Press: Ctrl+v and select the lines you want to comment:

Step 3: Shift–I#space (Enter Insert-at-left mode, type chars to insert. The selection will disappear, but all lines within it will be modified after Step 4.)

Step 4: Esc

one way manually

:set number
:10,12s/^/#

You could add the following mapping to your .vimrc

vnoremap <silent> # :s/^/#/<cr>:noh<cr>
vnoremap <silent> -# :s/^#//<cr>:noh<cr>

Highlight your block with:

Shift+v

# to comment your lines from the first column.

-# to uncomment the same way.

Highlight your block with: ShiftV

Comment the selected block out with: :norm i# (lower case i)

To uncomment, highlight your block again, and uncomment with: :norm ^x

The :norm command performs an action for every selected line. Commenting will insert a # at the start of every line, and uncommenting will delete that #.

I usually sweep out a visual block (<C-V>), then search and replace the first character with:

:'<,'>s/^/#

(Entering command mode with a visual block selected automatically places ‘<,’> on the command line) I can then uncomment the block by sweeping out the same visual block and:

:'<,'>s/^#//

There are some good plugins to help comment/uncomment lines. For example The NERD Commenter.

I have the following lines in my .vimrc:

" comment line, selection with Ctrl-N,Ctrl-N
au BufEnter *.py nnoremap  <C-N><C-N>    mn:s/^\(\s*\)#*\(.*\)/\1#\2/ge<CR>:noh<CR>`n
au BufEnter *.py inoremap  <C-N><C-N>    <C-O>mn<C-O>:s/^\(\s*\)#*\(.*\)/\1#\2/ge<CR><C-O>:noh<CR><C-O>`n
au BufEnter *.py vnoremap  <C-N><C-N>    mn:s/^\(\s*\)#*\(.*\)/\1#\2/ge<CR>:noh<CR>gv`n

" uncomment line, selection with Ctrl-N,N
au BufEnter *.py nnoremap  <C-N>n     mn:s/^\(\s*\)#\([^ ]\)/\1\2/ge<CR>:s/^#$//ge<CR>:noh<CR>`n
au BufEnter *.py inoremap  <C-N>n     <C-O>mn<C-O>:s/^\(\s*\)#\([^ ]\)/\1\2/ge<CR><C-O>:s/^#$//ge<CR><C-O>:noh<CR><C-O>`n
au BufEnter *.py vnoremap  <C-N>n     mn:s/^\(\s*\)#\([^ ]\)/\1\2/ge<CR>gv:s/#\n/\r/ge<CR>:noh<CR>gv`n

The shortcuts preserve your cursor position and your comments as long as they start with # (there is space after #). For example:

# variable x
x = 0

After commenting:

# variable x
#x = 0

After uncomennting:

# variable x
x = 0

Frankly I use a tcomment plugin for that link. It can handle almost every syntax. It defines nice movements, using it with some text block matchers specific for python makes it a powerful tool.

NERDcommenter is an excellent plugin for commenting which automatically detects a number of filetypes and their associated comment characters. Ridiculously easy to install using Pathogen.

Comment with <leader>cc. Uncomment with <leader>cu. And toggle comments with <leader>c<space>.

(The default <leader> key in vim is \)

There’s a lot of comment plugins for vim – a number of which are multi-language – not just python. If you use a plugin manager like Vundle then you can search for them (once you’ve installed Vundle) using e.g.:

:PluginSearch comment

And you will get a window of results. Alternatively you can just search vim-scripts for comment plugins.

No plugins or mappings required. Try the built-in “norm” command, which literally executes anything you want on every selected line.

Add # Comments

1. shift V to visually select lines
2. :norm i#

Remove # Comments

1. visually select region as before
2. :norm x

Or if your comments are indented you can do :norm ^x

Notice that these are just ordinary vim commands being preceded by “:norm” to execute them on each line.

More detailed answer for using “norm” command in one of the answers here

What’s a quick way to comment/uncomment lines in Vim?

A very minimal light weight plugin: vim-commentary.

gcc to comment a line
gcgc to uncomment. check out the plugin page for more.

v+k/j highlight the block then gcc to comment that block.

CtrlK for comment (Visual Mode):

vnoremap <silent> <C-k> :s#^#\##<cr>:noh<cr>

CtrlU for uncomment (Visual Mode):

vnoremap <silent> <C-u> :s#^\###<cr>:noh<cr>