[optparse] Change Uses of List[] to Sequence[] in argument positions. (#1179)

* Change Uses of List[] to Sequence[] in argument positions.

One of these (parse_args()) broke in real-world code, because the
expected type was List[Union[str, bytes]] but the actual type was
List[str] (because List is invariant).  That is ridiculous, so I
changed the accepted type to Sequence[_Text] which is covariant.  Then
I found a few other methods/functions that probably should also be
changed to Sequence, but I'm less certain of those.  I'm not at all
sure about the instance/class attributes, so I left those alone
(though I suspect those might also have to switch).

* Fixes suggested by code review

- Changed Sequence[Option] to Iterable[Option] everywhere
- Changed _process_args to plain List

stdlib/2and3/optparse.pyi

@@ -1,6 +1,6 @@
 # Generated by pytype, with only minor tweaks. Might be incomplete.
 import sys
-from typing import Any, Optional, List, Callable, Tuple, Dict, Iterable, Union, Mapping, IO
+from typing import Any, Callable, Dict, IO, Iterable, List, Mapping, Optional, Sequence, Tuple, Union
 
 # See https://groups.google.com/forum/#!topic/python-ideas/gA1gdj3RZ5g
 if sys.version_info >= (3,):
@@ -27,7 +27,7 @@ class BadOptionError(OptParseError):
 
 class AmbiguousOptionError(BadOptionError):
     possibilities = ...  # type: Iterable[_Text]
-    def __init__(self, opt_str: _Text, possibilities: List[_Text]) -> None: ...
+    def __init__(self, opt_str: _Text, possibilities: Sequence[_Text]) -> None: ...
 
 class OptionError(OptParseError):
     msg = ...  # type: _Text
@@ -136,7 +136,7 @@ class OptionContainer:
     def _create_option_mappings(self) -> None: ...
     def _share_option_mappings(self, parser: OptionParser) -> None: ...
     def add_option(self, *args, **kwargs) -> Any: ...
-    def add_options(self, option_list: List[Option]) -> None: ...
+    def add_options(self, option_list: Iterable[Option]) -> None: ...
     def destroy(self) -> None: ...
     def format_description(self, formatter: Optional[HelpFormatter]) -> Any: ...
     def format_help(self, formatter: Optional[HelpFormatter]) -> _Text: ...
@@ -171,7 +171,7 @@ class OptionParser(OptionContainer):
     values = ...  # type: Any
     version = ...  # type: _Text
     def __init__(self, usage: Optional[_Text] = ...,
-                       option_list: List[Option] = ...,
+                       option_list: Iterable[Option] = ...,
                        option_class: Option = ...,
                        version: Optional[_Text] = ...,
                        conflict_handler: _Text = ...,
@@ -187,8 +187,8 @@ class OptionParser(OptionContainer):
     def _get_args(self, args: Iterable) -> List[Any]: ...
     def _init_parsing_state(self) -> None: ...
     def _match_long_opt(self, opt: _Text) -> _Text: ...
-    def _populate_option_list(self, option_list: List[Option], add_help: bool = ...) -> None: ...
-    def _process_args(self, largs: List[_Text], rargs: List, values: Values) -> None: ...
+    def _populate_option_list(self, option_list: Iterable[Option], add_help: bool = ...) -> None: ...
+    def _process_args(self, largs: List, rargs: List, values: Values) -> None: ...
     def _process_long_opt(self, rargs: List, values: Any) -> None: ...
     def _process_short_opts(self, rargs: List, values: Any) -> None: ...
     def add_option_group(self, *args, **kwargs) -> OptionParser: ...
@@ -206,7 +206,7 @@ class OptionParser(OptionContainer):
     def get_prog_name(self) -> _Text: ...
     def get_usage(self) -> _Text: ...
     def get_version(self) -> _Text: ...
-    def parse_args(self, args: Optional[List[_Text]] = ..., values: Optional[Values] = ...) -> Tuple[Any, ...]: ...
+    def parse_args(self, args: Optional[Sequence[_Text]] = ..., values: Optional[Values] = ...) -> Tuple[Any, ...]: ...
     def print_usage(self, file: Optional[IO[str]] = ...) -> None: ...
     def print_help(self, file: Optional[IO[str]] = ...) -> None: ...
     def print_version(self, file: Optional[IO[str]] = ...) -> None: ...