Support additional unpacking generalisations (PEP 448)

[spkersten]

[JukkaL]

PEP text: https://www.python.org/dev/peps/pep-0448/

[mbdevpl]

I just would like to add that although the new parser (mentioned in #1353) parses below:

my_dict = {'b': 2, 'c': 3}
my_new_dict = {'a': 1, **my_dict}

mypy ends up in a bad place:

$ python3.5 -m mypy --fast-parser mypy_pep0448.py
Traceback (most recent call last):
  File "/home/mb/.local/lib/python3.5/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/home/mb/.local/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/__main__.py", line 5, in <module>
    main(None)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/main.py", line 54, in main
    res = type_check_only(sources, bin_dir, options)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/main.py", line 102, in type_check_only
    python_path=options.python_path)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 211, in build
    dispatch(sources, manager)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1334, in dispatch
    graph = load_graph(sources, manager)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1349, in load_graph
    st = State(id=bs.module, path=bs.path, source=bs.text, manager=manager)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1121, in __init__
    self.parse_file()
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1232, in parse_file
    self.tree = manager.parse_file(self.id, self.xpath, source)
  File "/home/mb/.local/lib/python3.5/contextlib.py", line 77, in __exit__
    self.gen.throw(type, value, traceback)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1186, in wrap_context
    yield
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 1232, in parse_file
    self.tree = manager.parse_file(self.id, self.xpath, source)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/build.py", line 452, in parse_file
    fast_parser=FAST_PARSER in self.flags)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/parse.py", line 88, in parse
    custom_typing_module=custom_typing_module)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 66, in parse
    ).visit(ast)
  File "/home/mb/.local/lib/python3.5/site-packages/typed_ast/ast35.py", line 252, in visit
    return visitor(node)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 228, in visit_Module
    body = self.fix_function_overloads(self.visit_list(mod.body))
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 129, in visit_list
    return [self.visit(e) for e in l]
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 129, in <listcomp>
    return [self.visit(e) for e in l]
  File "/home/mb/.local/lib/python3.5/site-packages/typed_ast/ast35.py", line 252, in visit
    return visitor(node)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 97, in wrapper
    node = f(self, ast)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 387, in visit_Assign
    self.visit(n.value),
  File "/home/mb/.local/lib/python3.5/site-packages/typed_ast/ast35.py", line 252, in visit
    return visitor(node)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 97, in wrapper
    node = f(self, ast)
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/fastparse.py", line 574, in visit_Dict
    return DictExpr(list(zip(self.visit_list(n.keys), self.visit_list(n.values))))
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/nodes.py", line 1445, in __init__
    for x in items):
  File "/home/mb/.local/lib/python3.5/site-packages/mypy/nodes.py", line 1445, in <genexpr>
    for x in items):
AttributeError: 'NoneType' object has no attribute 'literal'

for reference, using current parser:

$ python3.5 -m mypy mypy_pep0448.py
mypy_pep0448.py:2: error: Parse error before **

also for reference: Ubuntu 14.04 x64, Python 3.5.1, mypy 0.4.2, typed-ast 0.5.2