Enhance python_script to support "_getitem_"

In order to use dict / list structures in python scripts we need
_getitem_ allowed in the RestrictedPython environment. There is a
default_guarded_getitem included with RestrictedPython, which is a
pass through used in the Eval code paths.

homeassistant/components/python_script.py

@@ -65,6 +65,7 @@ def execute(hass, filename, source, data=None):
     from RestrictedPython import compile_restricted_exec
     from RestrictedPython.Guards import safe_builtins, full_write_guard
     from RestrictedPython.Utilities import utility_builtins
+    from RestrictedPython.Eval import default_guarded_getitem
 
     compiled = compile_restricted_exec(source, filename=filename)
 
@@ -99,6 +100,7 @@ def protected_getattr(obj, name, default=None):
         '_getattr_': protected_getattr,
         '_write_': full_write_guard,
         '_getiter_': iter,
+        '_getitem_': default_guarded_getitem
     }
     logger = logging.getLogger('{}.{}'.format(__name__, filename))
     local = {