Add pycodestyle Python linter support (#872)

Add a pycodestyle linter

ale_linters/python/pycodestyle.vim

@@ -0,0 +1,42 @@
+" Author: Michael Thiesen <micthiesen@gmail.com>
+" Description: pycodestyle linting for python files
+
+call ale#Set('python_pycodestyle_executable', 'pycodestyle')
+call ale#Set('python_pycodestyle_options', '')
+call ale#Set('python_pycodestyle_use_global', 0)
+
+function! ale_linters#python#pycodestyle#GetExecutable(buffer) abort
+    return ale#python#FindExecutable(a:buffer, 'python_pycodestyle', ['pycodestyle'])
+endfunction
+
+function! ale_linters#python#pycodestyle#GetCommand(buffer) abort
+    return ale#Escape(ale_linters#python#pycodestyle#GetExecutable(a:buffer))
+    \   . ' '
+    \   . ale#Var(a:buffer, 'python_pycodestyle_options')
+    \   . ' -'
+endfunction
+
+function! ale_linters#python#pycodestyle#Handle(buffer, lines) abort
+    let l:pattern = '\v^(\S*):(\d*):(\d*): ((([EW])\d+) .*)$'
+    let l:output = []
+
+    " lines are formatted as follows:
+    " file.py:21:26: W291 trailing whitespace
+    for l:match in ale#util#GetMatches(a:lines, l:pattern)
+        call add(l:output, {
+        \   'lnum': l:match[2] + 0,
+        \   'col': l:match[3] + 0,
+        \   'type': l:match[6],
+        \   'text': l:match[4],
+        \})
+    endfor
+
+    return l:output
+endfunction
+
+call ale#linter#Define('python', {
+\   'name': 'pycodestyle',
+\   'executable_callback': 'ale_linters#python#pycodestyle#GetExecutable',
+\   'command_callback': 'ale_linters#python#pycodestyle#GetCommand',
+\   'callback': 'ale_linters#python#pycodestyle#Handle',
+\})