Initial pass at learning vim's python interface.

.gitignore

+.*.swp
+*.pyc

plugin/cobol.vim

+" cobol.vim - Some useful COBOL scripts.
+" Maintainer:   Kevin Lyda <kevin@phrye.com>
+" Version:      0.1
+" TODO: add vim-scripts config
+
+if exists('g:loaded_cobol') || &cp
+  echo "Already loaded."
+  finish
+endif
+let g:loaded_cobol = 1
+
+if !has('python3')
+  echo "Missing python."
+  finish
+endif
+
+let s:path = fnamemodify(resolve(expand('<sfile>:p')), ':h')
+
+function! HelloWorld()
+  exec 'py3file ' . s:path . '/renumber.py'
+endfunction

plugin/renumber.py

+#! /usr/bin/env python3
+# -*- coding: utf-8 -*-
+# vim:fenc=utf-8
+#
+# Copyright © 2017 Kevin Lyda <kevin@phrye.com>
+#
+# Distributed under terms of the GPL license.
+
+"""
+COBOL utilities.
+"""
+
+import vim
+
+print(vim.current.buffer.name)
+b = vim.current.buffer
+for i in range(len(b)):
+  b[i] = 'moo ' + b[i]