python: Convert function type annotations to Python 3 style.

Generated by com2ann (slightly patched to avoid also converting
assignment type annotations, which require Python 3.6), followed by
some manual whitespace adjustment, and six fixes for runtime issues:

-    def __init__(self, token: Token, parent: Optional[Node]) -> None:
+    def __init__(self, token: Token, parent: "Optional[Node]") -> None:

-def main(options: argparse.Namespace) -> NoReturn:
+def main(options: argparse.Namespace) -> "NoReturn":

-def fetch_request(url: str, callback: Any, **kwargs: Any) -> Generator[Callable[..., Any], Any, None]:
+def fetch_request(url: str, callback: Any, **kwargs: Any) -> "Generator[Callable[..., Any], Any, None]":

-def assert_server_running(server: subprocess.Popen[bytes], log_file: Optional[str]) -> None:
+def assert_server_running(server: "subprocess.Popen[bytes]", log_file: Optional[str]) -> None:

-def server_is_up(server: subprocess.Popen[bytes], log_file: Optional[str]) -> bool:
+def server_is_up(server: "subprocess.Popen[bytes]", log_file: Optional[str]) -> bool:

-    method_kwarg_pairs: List[FuncKwargPair],
+    method_kwarg_pairs: "List[FuncKwargPair]",

Signed-off-by: Anders Kaseorg <anders@zulipchat.com>

tools/webpack

@@ -10,8 +10,7 @@ os.chdir(os.path.join(os.path.dirname(__file__), '..'))
 STATIC_PATH = 'static/'
 
 
-def build_for_prod_or_casper(quiet):
-    # type: (bool) -> NoReturn
+def build_for_prod_or_casper(quiet: bool) -> NoReturn:
     """Builds for production, writing the output to disk"""
 
     webpack_args = ['node', 'node_modules/.bin/webpack-cli',
@@ -22,8 +21,7 @@ def build_for_prod_or_casper(quiet):
         print('Starting webpack compilation')
     os.execvp(webpack_args[0], webpack_args)
 
-def build_for_dev_server(host, port, minify, disable_host_check):
-    # type: (str, str, bool, bool) -> None
+def build_for_dev_server(host: str, port: str, minify: bool, disable_host_check: bool) -> None:
     """watches and rebuilds on changes, serving files from memory via webpack-dev-server"""
 
     # This is our most dynamic configuration, which we use for our
@@ -68,8 +66,7 @@ def build_for_dev_server(host, port, minify, disable_host_check):
         webpack_process = subprocess.Popen(webpack_args)
 
         class WebpackConfigFileChangeHandler(pyinotify.ProcessEvent):
-            def process_default(self, event):
-                # type: (pyinotify.Event) -> None
+            def process_default(self, event: pyinotify.Event) -> None:
                 nonlocal webpack_process
                 print('Restarting webpack-dev-server due to config changes...')
                 webpack_process.terminate()
@@ -86,8 +83,7 @@ def build_for_dev_server(host, port, minify, disable_host_check):
         webpack_process.terminate()
         webpack_process.wait()
 
-def build_for_most_tests():
-    # type: () -> None
+def build_for_most_tests() -> None:
     """Generates a stub asset stat file for django so backend test can render a page"""
 
     # Tests like test-backend, test-api, and test-home-documentation use