Fix #680 - Use --shadow-file to check for problems with mypy while you type

autoload/ale/fixers/autopep8.vim

@@ -12,7 +12,7 @@ function! ale#fixers#autopep8#Fix(buffer) abort
     \   ['/bin/autopep8'],
     \)
 
-    if empty(l:executable)
+    if !executable(l:executable)
         return 0
     endif
 

autoload/ale/fixers/isort.vim

@@ -11,7 +11,7 @@ function! ale#fixers#isort#Fix(buffer) abort
     \   ['/bin/isort'],
     \)
 
-    if empty(l:executable)
+    if !executable(l:executable)
         return 0
     endif
 

autoload/ale/fixers/yapf.vim

@@ -11,7 +11,7 @@ function! ale#fixers#yapf#Fix(buffer) abort
     \   ['/bin/yapf'],
     \)
 
-    if empty(l:executable)
+    if !executable(l:executable)
         return 0
     endif
 

autoload/ale/python.vim

@@ -58,11 +58,5 @@ function! ale#python#FindExecutable(buffer, base_var_name, path_list) abort
         endfor
     endif
 
-    let l:global_executable = ale#Var(a:buffer, a:base_var_name . '_executable')
-
-    if executable(l:global_executable)
-        return l:global_executable
-    endif
-
-    return ''
+    return ale#Var(a:buffer, a:base_var_name . '_executable')
 endfunction