Fix Mutable default argument

Python’s default arguments are evaluated once when the function is defined,
not each time the function is called. This means that if you use a mutable
default argument (like list and dict) and mutate it, you will and have mutated
that object for all future calls to the function as well.

more details about this wrong usage here:
http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments

Change-Id: If187f16bfb305ac4fe6e4177e498a06c49c3f946

Author: ting.wang

openstackclient/common/utils.py

@@ -163,7 +163,7 @@ def get_field(item, field):
         raise exceptions.CommandError(msg)
 
 
-def get_item_properties(item, fields, mixed_case_fields=[], formatters={}):
+def get_item_properties(item, fields, mixed_case_fields=None, formatters=None):
     """Return a tuple containing the item properties.
 
     :param item: a single item resource (e.g. Server, Project, etc)
@@ -172,6 +172,11 @@ def get_item_properties(item, fields, mixed_case_fields=[], formatters={}):
     :param formatters: dictionary mapping field names to callables
        to format the values
     """
+    if mixed_case_fields is None:
+        mixed_case_fields = []
+    if formatters is None:
+        formatters = {}
+
     row = []
 
     for field in fields:
@@ -187,7 +192,7 @@ def get_item_properties(item, fields, mixed_case_fields=[], formatters={}):
     return tuple(row)
 
 
-def get_dict_properties(item, fields, mixed_case_fields=[], formatters={}):
+def get_dict_properties(item, fields, mixed_case_fields=None, formatters=None):
     """Return a tuple containing the item properties.
 
     :param item: a single dict resource
@@ -196,6 +201,11 @@ def get_dict_properties(item, fields, mixed_case_fields=[], formatters={}):
     :param formatters: dictionary mapping field names to callables
        to format the values
     """
+    if mixed_case_fields is None:
+        mixed_case_fields = []
+    if formatters is None:
+        formatters = {}
+
     row = []
 
     for field in fields: