Traceback analysing asyncio "item = yield from queue.get()" #836

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1. gjcarneiro

   added a commit that references this issue on Aug 20, 2015

   Added basic asyncio.queues stubs

   5aee184
2. rockneurotiko commented on Aug 20, 2015

   

   rockneurotiko

   on Aug 20, 2015

   Contributor

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

   added

   bugmypy got something wrongmypy got something wrong

   on Aug 20, 2015
4. JukkaL commented on Aug 20, 2015

   

   JukkaL

   on Aug 20, 2015

   Collaborator

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   Thanks for reporting this! I was able to reproduce the issue.
5. vitawasalreadytaken commented on Aug 21, 2015

   

   vitawasalreadytaken

   on Aug 21, 2015

   Contributor

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   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.
6. nierob commented on Sep 10, 2015

   

   nierob

   on Sep 10, 2015

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   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'
   
7. rockneurotiko

   added a commit that references this issue on Sep 10, 2015

   Fix when yield from was made of an AnyType (python#868, the generic e…

   ...

   45ff97a
8. gvanrossum

   closed this as completedin #1137on Jan 20, 2016