bring dynamodb2 update expression handling closer to spec

moto/dynamodb2/models.py

@@ -3,6 +3,7 @@ from collections import defaultdict
 import datetime
 import decimal
 import json
+import re
 
 from moto.compat import OrderedDict
 from moto.core import BaseBackend
@@ -110,15 +111,10 @@ class Item(object):
         }
 
     def update(self, update_expression, expression_attribute_names, expression_attribute_values):
-        ACTION_VALUES = ['SET', 'set', 'REMOVE', 'remove']
-
-        action = None
-        for value in update_expression.split():
-            if value in ACTION_VALUES:
-                # An action
-                action = value
-                continue
-            else:
+        parts = [p for p in re.split(r'\b(SET|REMOVE|ADD|DELETE)\b', update_expression) if p]
+        for action, valstr in zip(parts[:-1:1], parts[1::1]):
+            values = valstr.split(',')
+            for value in values:
                 # A Real value
                 value = value.lstrip(":").rstrip(",")
                 for k, v in expression_attribute_names.items():
@@ -127,6 +123,8 @@ class Item(object):
                     self.attrs.pop(value, None)
                 elif action == 'SET' or action == 'set':
                     key, value = value.split("=")
+                    key = key.strip()
+                    value = value.strip()
                     if value in expression_attribute_values:
                         self.attrs[key] = DynamoType(expression_attribute_values[value])
                     else: