refine syntax in Series rename method, and add docstring to validate_bool_kwarg

Author: rforgione

pandas/core/series.py

@@ -2355,10 +2355,8 @@ def align(self, other, join='outer', axis=None, level=None, copy=True,
 
     @Appender(generic._shared_docs['rename'] % _shared_doc_kwargs)
     def rename(self, index=None, **kwargs):
-        if 'inplace' in kwargs:
-            kwargs['inplace'] = validate_bool_kwarg(kwargs['inplace'], 'inplace')
-        else:
-            kwargs['inplace'] = False
+        kwargs['inplace'] = validate_bool_kwarg(kwargs.get('inplace', False),
+            'inplace')
 
         non_mapping = is_scalar(index) or (is_list_like(index) and
                                            not is_dict_like(index))

pandas/util/validators.py

@@ -217,6 +217,7 @@ def validate_args_and_kwargs(fname, args, kwargs,
     validate_kwargs(fname, kwargs, compat_args)
 
 def validate_bool_kwarg(value, arg_name):
+    """ Ensures that argument passed in arg_name is of type bool. """
     if not (is_bool(value) or value is None):
         raise ValueError('For argument "%s" expected type bool, ' % arg_name +\
             'received type %s.' % type(value).__name__)