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>

scripts/lib/hash_reqs.py

@@ -5,8 +5,7 @@ import argparse
 import hashlib
 from typing import Iterable, List, MutableSet
 
-def expand_reqs_helper(fpath, visited):
-    # type: (str, MutableSet[str]) -> List[str]
+def expand_reqs_helper(fpath: str, visited: MutableSet[str]) -> List[str]:
     if fpath in visited:
         return []
     else:
@@ -27,8 +26,7 @@ def expand_reqs_helper(fpath, visited):
                 result.append(dep)
     return result
 
-def expand_reqs(fpath):
-    # type: (str) -> List[str]
+def expand_reqs(fpath: str) -> List[str]:
     """
     Returns a sorted list of unique dependencies specified by the requirements file `fpath`.
     Removes comments from the output and recursively visits files specified inside `fpath`.
@@ -38,13 +36,11 @@ def expand_reqs(fpath):
     output = expand_reqs_helper(absfpath, set())
     return sorted(set(output))
 
-def hash_deps(deps):
-    # type: (Iterable[str]) -> str
+def hash_deps(deps: Iterable[str]) -> str:
     deps_str = "\n".join(deps) + "\n"
     return hashlib.sha1(deps_str.encode('utf-8')).hexdigest()
 
-def main():
-    # type: () -> int
+def main() -> int:
     description = ("Finds the SHA1 hash of list of dependencies in a requirements file"
                    " after recursively visiting all files specified in it.")
     parser = argparse.ArgumentParser(description=description)