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/lib/test_server.py

@@ -23,8 +23,7 @@ if TOOLS_DIR not in sys.path:
 from zerver.lib.test_fixtures import update_test_databases_if_required
 from scripts.lib.zulip_tools import get_or_create_dev_uuid_var_path
 
-def set_up_django(external_host):
-    # type: (str) -> None
+def set_up_django(external_host: str) -> None:
     os.environ['EXTERNAL_HOST'] = external_host
     os.environ["TORNADO_SERVER"] = "http://127.0.0.1:9983"
     os.environ["LOCAL_UPLOADS_DIR"] = get_or_create_dev_uuid_var_path(
@@ -33,8 +32,7 @@ def set_up_django(external_host):
     django.setup()
     os.environ['PYTHONUNBUFFERED'] = 'y'
 
-def assert_server_running(server, log_file):
-    # type: (subprocess.Popen[bytes], Optional[str]) -> None
+def assert_server_running(server: "subprocess.Popen[bytes]", log_file: Optional[str]) -> None:
     """Get the exit code of the server, or None if it is still running."""
     if server.poll() is not None:
         message = 'Server died unexpectedly!'
@@ -42,8 +40,7 @@ def assert_server_running(server, log_file):
             message += '\nSee %s\n' % (log_file,)
         raise RuntimeError(message)
 
-def server_is_up(server, log_file):
-    # type: (subprocess.Popen[bytes], Optional[str]) -> bool
+def server_is_up(server: "subprocess.Popen[bytes]", log_file: Optional[str]) -> bool:
     assert_server_running(server, log_file)
     try:
         # We could get a 501 error if the reverse proxy is up but the Django app isn't.