Traceback analysing asyncio "item = yield from queue.get()"

[gjcarneiro]

Analysing:

import asyncio

@asyncio.coroutine
def test(self):
    queue = asyncio.Queue(16384)
    sample = yield from queue.get()

Result:

  File "/home/gjc/projects/mollytest/env/lib/python3.4/site-packages/mypy/checker.py", line 1693, in visit_yield_from_expr
    if result_instance.type.fullname() == "asyncio.futures.Future":
AttributeError: 'AnyType' object has no attribute 'type'

[rockneurotiko]

That's probably because queue.get() should return a Future[T] or Future[Any], not Any.

[JukkaL]

Thanks for reporting this! I was able to reproduce the issue.

[vitawasalreadytaken]

I'm not familiar with mypy internals but I stepped through the analysis of this in pdb and found a couple of things:

1. The function is dynamically typed (there's a flag in TypeChecker.dynamic_funcs) so local variables apparently default to type Any. Fix: def test_get(self) -> None:
2. My Queue.get stub indeed has an incorrect return type as pointed out by @rockneurotiko. Fix: def get(self) -> Future[T]: ... in queues.pyi.
3. Mypy does not infer that queue is of type asyncio.Queue from this line: queue = asyncio.Queue(16384) (it is just Any). No idea why, but this fixes it: queue = asyncio.Queue(16384) # type: asyncio.Queue.

Only after all three fixes are applied the attribute error goes away.

I'm submitting a PR with fixed Queue stubs (Queue.put also needs to return Future instead of None). By the way, analyzing

@asyncio.coroutine
def test_put(self) -> None:
    queue = asyncio.Queue(16384)
    yield from queue.put(123)

does tell me that I need a type annotation for queue, unlike the get test which fails with the above AttributeError.

q.py: note: In function "test_put":
q.py:11: error: Need type annotation for variable
q.py:12: error: Iterable function return type expected for "yield from"

Again, it works if I explicitly add # type: asyncio.Queue. This baffles me because I expected mypy to detect the type automatically.

[nierob]

I think the problem is more generic:

import asyncio
import typing

@asyncio.coroutine
def foo(a):
   b = yield from a
   return b

gives me:

Traceback (most recent call last):
  File "/usr/local/bin/mypy", line 169, in <module>
    main()
  File "/usr/local/bin/mypy", line 34, in main
    type_check_only(path, module, bin_dir, options)
  File "/usr/local/bin/mypy", line 78, in type_check_only
    python_path=options.python_path)
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 164, in build
    result = manager.process(UnprocessedFile(info, program_text))
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 341, in process
    next.process()
  File "/usr/local/lib/python3.4/dist-packages/mypy/build.py", line 814, in process
    self.type_checker().visit_file(self.tree, self.tree.path)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 349, in visit_file
    self.accept(d)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 356, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 363, in accept
    return visitor.visit_decorator(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 1661, in visit_decorator
    e.func.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 332, in accept
    return visitor.visit_func_def(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 445, in visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 477, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 545, in check_func_def
    self.accept_in_frame(item.body)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 369, in accept_in_frame
    answer = self.accept(node, type_context)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 356, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 504, in accept
    return visitor.visit_block(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 934, in visit_block
    self.accept(s)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 356, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 543, in accept
    return visitor.visit_assignment_stmt(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 943, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type == None)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 971, in check_assignment
    self.infer_variable_type(inferred, lvalue, self.accept(rvalue),
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 356, in accept
    typ = node.accept(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/nodes.py", line 947, in accept
    return visitor.visit_yield_from_expr(self)
  File "/usr/local/lib/python3.4/dist-packages/mypy/checker.py", line 1708, in visit_yield_from_expr
    if result_instance.type.fullname() == "asyncio.futures.Future":
AttributeError: 'AnyType' object has no attribute 'type'