Move all functions for fixing things to autoload/ale/fixers, and only accept the lines of input where needed.

autoload/ale/fixers/generic_python.vim

@@ -0,0 +1,22 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: Generic fixer functions for Python.
+
+" Add blank lines before control statements.
+function! ale#fixers#generic_python#AddLinesBeforeControlStatements(buffer, lines) abort
+    let l:new_lines = []
+    let l:last_indent_size = 0
+
+    for l:line in a:lines
+        let l:indent_size = len(matchstr(l:line, '^ *'))
+
+        if l:indent_size <= l:last_indent_size
+        \&& match(l:line, '\v^ *(return|if|for|while|break|continue)') >= 0
+            call add(l:new_lines, '')
+        endif
+
+        call add(l:new_lines, l:line)
+        let l:last_indent_size = l:indent_size
+    endfor
+
+    return l:new_lines
+endfunction