Internal error when unpacking (asterisk) is used in a list

[jirutka]

tail = ['b', 'c']
['a', *tail]

Traceback (most recent call last):
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/local/lib/python3.5/site-packages/mypy/__main__.py", line 5, in <module>
    main(None)
  File "/usr/local/lib/python3.5/site-packages/mypy/main.py", line 40, in main
    res = type_check_only(sources, bin_dir, options)
  File "/usr/local/lib/python3.5/site-packages/mypy/main.py", line 81, in type_check_only
    options=options)
  File "/usr/local/lib/python3.5/site-packages/mypy/build.py", line 177, in build
    dispatch(sources, manager)
  File "/usr/local/lib/python3.5/site-packages/mypy/build.py", line 1323, in dispatch
    process_graph(graph, manager)
  File "/usr/local/lib/python3.5/site-packages/mypy/build.py", line 1461, in process_graph
    process_stale_scc(graph, scc)
  File "/usr/local/lib/python3.5/site-packages/mypy/build.py", line 1538, in process_stale_scc
    graph[id].type_check()
  File "/usr/local/lib/python3.5/site-packages/mypy/build.py", line 1301, in type_check
    manager.type_checker.visit_file(self.tree, self.xpath)
  File "/usr/local/lib/python3.5/site-packages/mypy/checker.py", line 152, in visit_file
    self.accept(d)
  File "/usr/local/lib/python3.5/site-packages/mypy/checker.py", line 201, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.5/site-packages/mypy/nodes.py", line 737, in accept
    return visitor.visit_expression_stmt(self)
  File "/usr/local/lib/python3.5/site-packages/mypy/checker.py", line 1333, in visit_expression_stmt
    self.accept(s.expr)
  File "/usr/local/lib/python3.5/site-packages/mypy/checker.py", line 201, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.5/site-packages/mypy/nodes.py", line 1445, in accept
    return visitor.visit_list_expr(self)
  File "/usr/local/lib/python3.5/site-packages/mypy/checker.py", line 1859, in visit_list_expr
    return self.expr_checker.visit_list_expr(e)
  File "/usr/local/lib/python3.5/site-packages/mypy/checkexpr.py", line 1283, in visit_list_expr
    e)
  File "/usr/local/lib/python3.5/site-packages/mypy/checkexpr.py", line 1303, in check_list_or_set_expr
    [nodes.ARG_POS] * len(items), context)[0]
  File "/usr/local/lib/python3.5/site-packages/mypy/checkexpr.py", line 253, in check_call
    messages=arg_messages)
  File "/usr/local/lib/python3.5/site-packages/mypy/checkexpr.py", line 677, in check_argument_types
    actual + 1, i + 1, callee, context, messages)
  File "/usr/local/lib/python3.5/site-packages/mypy/checkexpr.py", line 702, in check_arg
    elif not is_subtype(caller_type, callee_type):
  File "/usr/local/lib/python3.5/site-packages/mypy/subtypes.py", line 51, in is_subtype
    return left.accept(SubtypeVisitor(right, type_parameter_checker))
AttributeError: 'NoneType' object has no attribute 'accept'

*** INTERNAL ERROR ***

unpacking.py:3: error: Internal error -- please report a bug at https://github.com/python/mypy/issues

NOTE: you can use "mypy --pdb ..." to drop into the debugger when this happens.

Related to #704.

[gvanrossum]

I guess we either have to support PEP 448 or at least defend against the crash.

FWIW I debugged the crash a bit and it has already issued the error "Can use starred expression only as assignment target", but apparently it barrels on and tries to call check_arg() with the None that came from failing to infer the starred expression's type.

I'll just put in a None check to avoid this.

[jirutka]

@gvanrossum When do you plan to release the version with this fix?

[gvanrossum]

Probably in 5-6 weeks. Until then you can install straight from the repo.

--Guido (mobile)

On Jul 21, 2016 9:05 AM, "Jakub Jirutka" [email protected] wrote:

@gvanrossum https://github.com/gvanrossum When do you plan to release
the version with this fix?

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