Prevent dictionary size from changing while iterating over its items

In Python 3, dict.items() returns 'a dict_item'. Iterating over it while
deleting some of the dictionary elements is forbidden. We have to iterate over
a list to avoid getting this error:

    RuntimeError: dictionary changed size during iteration

Change-Id: I43401e6eb9a31148fda4677644bf99e1b739d0dd

keystoneclient/base.py

@@ -51,23 +51,21 @@ def getid(obj):
 def filter_kwargs(f):
     @functools.wraps(f)
     def func(*args, **kwargs):
-        for key, ref in kwargs.items():
+        new_kwargs = {}
+        for key, ref in six.iteritems(kwargs):
             if ref is None:
                 # drop null values
-                del kwargs[key]
                 continue
 
             id_value = getid(ref)
-            if id_value == ref:
-                continue
+            if id_value != ref:
+                # If an object with an id was passed, then use the id, e.g:
+                #     user: user(id=1) becomes user_id: 1
+                key = '%s_id' % key
 
-            # if an object with an id was passed remove the object
-            # from params and replace it with just the id.
-            # e.g user: User(id=1) becomes user_id: 1
-            del kwargs[key]
-            kwargs['%s_id' % key] = id_value
+            new_kwargs[key] = id_value
 
-        return f(*args, **kwargs)
+        return f(*args, **new_kwargs)
     return func