add arg_directory; tests valid directory argument

example/aitf/argparsetools.py

@@ -69,6 +69,12 @@ def add_cache_dir_arg(parser):
         default=CACHE_DEFAULT
         )
 
+def arg_directory(arg):
+    if not os.path.exists(arg):
+        argerror('The directory "{0}" does not exist'.format(arg))
+    if not os.path.isdir(arg):
+        argerror('The path "{0}" is not a directory'.format(arg))
+    return os.path.abspath(arg)
 
 def arg_valid_cache_dir(arg):
     if arg == CACHE_INVALID: