Making a box in vim via python

Question

I am attempting to learn more about scripting Vim and writing plugins with python, but I'm having trouble getting started. Although I've read :h python (first step, read the manual), I had trouble parsing it.

So I thought it would be a good idea to try to understand a very simple python plugin. In this question, a user wants to make a box like

################################################################################
#################################### LOAD ######################################
################################################################################

around words that they type.

How can we do this in vim through python?

Specifically, I would like to write a function MyPythonFunction() and be able to have the line

some words

with my cursor on that line, perform :call MyPythonFunction(), and have this function (written as much as possible in python) create the block of hashes with the line of text centered in the middle row.

Answer 1

To use Python in Vim, your Vim must be compiled with support for it. Most Linux distributions (Debian-based, CentOS, Arch, for example) have support for Python2, but not for Python3. To check for Python support you can use:

:echo has('python')
:echo has('python3')

If it echoes 1, it means Vim has this feature (python is Python 2). If it echoes 0, it means Vim doesn't have this feature.

---

The simplest way to use Python is to do:

:python some statement

However, this will become unwieldy very quickly, so instead we can do:

:python <<EOF
print('it is an')
print('ex-parrot')
EOF

---

Now, to get to the question. This can be accomplished using a fairly simple function:

function! PythonBox()
    python <<EOF
import vim
this_buffer = vim.current.buffer
(row,col)   = vim.current.window.cursor
this_line   = vim.current.line
this_buffer.append ('#'*80, row - 1)
this_buffer[row] = '{:#^80}'.format(' ' + this_line + ' ')
this_buffer.append ('#'*80, row + 1)
EOF
endfunction

Notes:

• import vim only works when loaded in vim.
• vim.current.buffer, vim.current.window and vim.current.line are exactly what they sound like.
• vim.current.buffer is list-like and mutable, with each line a member. The list is indexed from 0, so line 1 is vim.current.buffer[0].
• We can add a line to a buffer using

  buffer.append(str [, linenum])

• Aligning and padding the line is fairly simple with str.format.