Problem with dangling comma

[srittau]

From python/typeshed#3358, CI: https://travis-ci.org/python/typeshed/jobs/597311318

Please consider the following file foo.pyi:

ExceptHookArgs = NamedTuple(
    "ExceptHookArgs",
    [
        ("exc_type", Type[BaseException]),
        ("exc_value", Optional[BaseException]),
        ("exc_traceback", Optional[TracebackType]),
        ("thread", Optional[Thread]),
    ],
)

pytype 2019.09.17 (Python 3.7.3) complains:

$ pytype-single --parse-pyi --module-name=foo -V3.6 foo.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 ',', expecting ')'

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: "foo.pyi", line 8
    ],
     ^
ParseError: syntax error, unexpected ',', expecting ')'

I can work around this for now, but black will re-insert the comma, so that will cause us problems in the future.