Empty tuple syntax

[srittau]

I seem to have a knack for uncovering pytype snags with my typeshed PRs. This time it's python/typeshed#3351. CI failure: https://travis-ci.org/python/typeshed/jobs/597038126

Running pytype manually I get the following output:

$ pytype-single --parse-pyi --module-name=multiprocessing.shared_memory -V3.6 stdlib/3/multiprocessing/shared_memory.pyi 
Traceback (most recent call last):
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/pyi/parser.py", line 430, in parse
    defs = parser_ext.parse(self, src)
pytype.pyi.parser.ParseError: ParseError: syntax error, unexpected ')'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./.venv/bin/pytype-single", line 11, in <module>
    load_entry_point('pytype==2019.9.17', 'console_scripts', 'pytype-single')()
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/main.py", line 88, in main
    return _run_pytype(options)
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/main.py", line 96, in _run_pytype
    unused_ast = io.parse_pyi(options)
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/io.py", line 263, in parse_pyi
    ast = loader.load_file(options.module_name, options.input)
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/load_pytd.py", line 241, in load_file
    python_version=self.python_version)
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/pyi/parser.py", line 1250, in parse_file
    src, name, filename)
  File "/home/srittau/Projekte/typeshed/.venv/lib/python3.7/site-packages/pytype/pyi/parser.py", line 440, in parse
    column=self._error_location[1], text=text)
pytype.pyi.parser.ParseError:   File: "stdlib/3/multiprocessing/shared_memory.pyi", line 24
    def __reduce__(self: _S) -> Tuple[_S, Tuple[()]]: ...
                                                 ^

I assume, pytype does not support PEP 484's empty tuple syntax yet (Tuple[()]).

[rchen152]

Well, it's a little embarrassing that our parser keeps throwing up =(
I think I've fixed all the issues that came up, pending a GitHub sync and release.