use a own namespace for exec command

src/martian/directive.py

@@ -245,9 +245,10 @@ def __init__(self, *args, **kw):
     def check_factory_signature(self, *arguments, **kw):
         args, varargs, varkw, defaults = inspect.getargspec(self.factory)
         argspec = inspect.formatargspec(args[1:], varargs, varkw, defaults)
-        exec("def signature_checker" + argspec + ": pass")
+        ns = dict()
+        exec("def signature_checker" + argspec + ": pass", dict(), ns)
         try:
-            locals()['signature_checker'](*arguments, **kw)
+            ns['signature_checker'](*arguments, **kw)
         except TypeError as e:
             message = e.args[0]
             message = message.replace("signature_checker()", self.name)

src/martian/util.py

@@ -28,7 +28,7 @@
 def not_unicode_or_ascii(value):
 
     # python3 compatibility
-    if sys.version_info < (3,) and  isinstance(value, unicode):
+    if sys.version_info < (3,) and isinstance(value, unicode):
         return False
     if not isinstance(value, str):
         return True