Fixing flake8 B errors

.flake8

@@ -14,17 +14,15 @@
 #    44 E127 continuation line over-indented for visual indent
 
 [flake8]
-ignore = F401, F811, E127, E128, E301, E302, E305, E501, E701, E704
+ignore = F401, F811, E127, E128, E301, E302, E305, E501, E701, E704, B303
 
 # Errors that we need to fix before enabling flake8 by default:
 #   921 F821 undefined name
 #    28 E116 unexpected indentation (comment)
 #    26 F403 from * import used
 #    14 E251 unexpected spaces around keyword argument '='
-#     8 B006 mutable argument defaults
 #     7 E999 invalid syntax
 #     7 E111 indentation is not a multiple of four
 #     5 F405 name undefined or from * imports
 #     4 E262 inline comment should start with #
 #     4 E114 indentation is not a multiple of four
-#     2 B303 __metaclass__ use on Python 3

stdlib/3/builtins.pyi

@@ -787,8 +787,8 @@ def zip(iter1: Iterable[_T1], iter2: Iterable[_T2],
 def zip(iter1: Iterable[_T1], iter2: Iterable[_T2], iter3: Iterable[_T3],
         iter4: Iterable[_T4]) -> Iterator[Tuple[_T1, _T2,
                                                _T3, _T4]]: ...  # TODO more than four iterables
-def __import__(name: str, globals: Dict[str, Any] = {}, locals: Dict[str, Any] = {},
-               fromlist: List[str] = [], level: int = -1) -> Any: ...
+def __import__(name: str, globals: Dict[str, Any] = ..., locals: Dict[str, Any] = ...,
+               fromlist: List[str] = ..., level: int = -1) -> Any: ...
 
 # Ellipsis
 

stdlib/3/configparser.pyi

@@ -129,7 +129,7 @@ class ConfigParser(RawConfigParser):
                  empty_lines_in_values: bool = ...,
                  default_section: str = ...,
                  interpolation: Interpolation = None,
-                 converters: _converters = {}) -> None: ...
+                 converters: _converters = ...) -> None: ...
 
 
 class Error(Exception):

stdlib/3/multiprocessing/__init__.pyi

@@ -23,11 +23,11 @@ class Pool():
     def apply(self,
               func: Callable[..., Any],
               args: Iterable[Any]=(),
-              kwds: Dict[str, Any]={}) -> Any: ...
+              kwds: Dict[str, Any]=...) -> Any: ...
     def apply_async(self,
                 func: Callable[..., Any],
                 args: Iterable[Any]=(),
-                kwds: Dict[str, Any]={},
+                kwds: Dict[str, Any]=...,
                 callback: Callable[..., None] = None,
                 error_callback: Callable[[BaseException], None] = None) -> AsyncResult: ...
     def map(self,

stdlib/3/multiprocessing/pool.pyi

@@ -17,11 +17,11 @@ class ThreadPool():
     def apply(self,
               func: Callable[..., Any],
               args: Iterable[Any]=(),
-              kwds: Dict[str, Any]={}) -> Any: ...
+              kwds: Dict[str, Any]=...) -> Any: ...
     def apply_async(self,
                 func: Callable[..., Any],
                 args: Iterable[Any]=(),
-                kwds: Dict[str, Any]={},
+                kwds: Dict[str, Any]=...,
                 callback: Callable[..., None] = None,
                 error_callback: Callable[[BaseException], None] = None) -> AsyncResult: ...
     def map(self,