runtime error (StopIteration) due to _inference_tip_cached KeyError under py3.7 but not py3.6

[timb07]

I've encountered a very similar runtime error as the one in #2937. I've confirmed that the two code samples in that issue to reproduce the problem both work in my environment, so it's not a regression of that specific issue. Further, the problem appears under Python 3.7 but not under Python 3.6 (with the same versions of pylint and astroid for both).

There are no preview releases of pylint or astroid at the moment to check with.

Steps to reproduce

1. $ python3.7 -mvenv venv
2. $ . venv/bin/activate
3. $ pip install pylint objectpath
4. $ pylint -j1 objectpath_pylint.py where objectpath_pylint.py is:

from objectpath import Tree

def foobar():
    count = 0
    while True:
        tree = Tree({})
        count += tree.execute('')
        if count:
            break

(That's the minimal case to reproduce the issue, based on the original code the issue appeared in.)

Current behavior

************* Module objectpath_pylint
objectpath_pylint.py:1:0: C0114: Missing module docstring (missing-module-docstring)
objectpath_pylint.py:3:0: C0116: Missing function or method docstring (missing-function-docstring)
Traceback (most recent call last):
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/__init__.py", line 91, in _inference_tip_cached
    return iter(_cache[func, node])
KeyError: (<function register_builtin_transform.<locals>._transform_wrapper at 0x7fe0e17a98c0>, <Call l.551 at 0x7fe0e1099f10>)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/scoped_nodes.py", line 1677, in infer_call_result
    yield from returnnode.value.infer(context)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/node_classes.py", line 353, in infer
    return self._explicit_inference(self, context, **kwargs)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/__init__.py", line 93, in _inference_tip_cached
    result = func(*args, **kwargs)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/brain/brain_builtin_inference.py", line 129, in _transform_wrapper
    result = transform(node, context=context)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/brain/brain_builtin_inference.py", line 716, in infer_int
    first_value = next(call.positional_arguments[0].infer(context=context))
StopIteration

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/tim/dev/pylint/venv/bin/pylint", line 11, in <module>
    sys.exit(run_pylint())
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/__init__.py", line 23, in run_pylint
    PylintRun(sys.argv[1:])
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/lint.py", line 1731, in __init__
    linter.check(args)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/lint.py", line 1004, in check
    self._do_check(files_or_modules)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/lint.py", line 1165, in _do_check
    self.check_astroid_module(ast_node, walker, rawcheckers, tokencheckers)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/lint.py", line 1252, in check_astroid_module
    walker.walk(ast_node)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/utils/ast_walker.py", line 77, in walk
    self.walk(child)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/utils/ast_walker.py", line 77, in walk
    self.walk(child)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/utils/ast_walker.py", line 77, in walk
    self.walk(child)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/utils/ast_walker.py", line 74, in walk
    callback(astroid)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/checkers/base.py", line 1024, in visit_if
    self._check_using_constant_test(node, node.test)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/checkers/base.py", line 1062, in _check_using_constant_test
    inferred = utils.safe_infer(test)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/pylint/checkers/utils.py", line 1084, in safe_infer
    value = next(inferit)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 131, in raise_if_nothing_inferred
    yield next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 95, in wrapped
    res = next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/bases.py", line 133, in _infer_stmts
    for inferred in stmt.infer(context=context):
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/util.py", line 160, in limit_inference
    yield from islice(iterator, size)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/context.py", line 113, in cache_generator
    for result in generator:
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 131, in raise_if_nothing_inferred
    yield next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 95, in wrapped
    res = next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/util.py", line 160, in limit_inference
    yield from islice(iterator, size)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/context.py", line 113, in cache_generator
    for result in generator:
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 131, in raise_if_nothing_inferred
    yield next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 95, in wrapped
    res = next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/inference.py", line 468, in _filter_operation_errors
    for result in infer_callable(self, context):
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/inference.py", line 787, in _infer_augassign
    for lhs, rhs in itertools.product(lhs_iter, rhs_iter):

[Many repeated sequences of the some of the above lines omitted]

  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/util.py", line 160, in limit_inference
    yield from islice(iterator, size)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/context.py", line 113, in cache_generator
    for result in generator:
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 141, in raise_if_nothing_inferred
    yield from generator
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 95, in wrapped
    res = next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/inference.py", line 227, in infer_call
    yield from callee.infer_call_result(caller=self, context=callcontext)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/scoped_nodes.py", line 1677, in infer_call_result
    yield from returnnode.value.infer(context)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/util.py", line 160, in limit_inference
    yield from islice(iterator, size)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/context.py", line 113, in cache_generator
    for result in generator:
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 141, in raise_if_nothing_inferred
    yield from generator
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/decorators.py", line 95, in wrapped
    res = next(generator)
  File "/home/tim/dev/pylint/venv/lib/python3.7/site-packages/astroid/inference.py", line 227, in infer_call
    yield from callee.infer_call_result(caller=self, context=callcontext)
RuntimeError: generator raised StopIteration

Expected behavior

************* Module objectpath_pylint
objectpath_pylint.py:1:0: C0114: Missing module docstring (missing-module-docstring)
objectpath_pylint.py:3:0: C0116: Missing function or method docstring (missing-function-docstring)

-----------------------------------
Your code has been rated at 7.50/10

That's the behaviour under Python 3.6; here's the pylint --version output for the above expected behaviour

pylint 2.4.4
astroid 2.3.3
Python 3.6.9 (default, Nov  7 2019, 10:44:02) 
[GCC 8.3.0]

pylint --version output

pylint 2.4.4
astroid 2.3.3
Python 3.7.5 (default, Nov  7 2019, 10:50:52) 
[GCC 8.3.0]

[PCManticore]

Hey @timb07 Thank you for the report!

I'm trying to reproduce this locally but there seems to be something missing. I tried with 3.6, 3.7 and 3.8 with the same library versions as you, e.g.

pylint 2.4.4
astroid 2.3.3
Python 3.6.5 (default, May  7 2018, 10:07:07)
[GCC 4.2.1 Compatible Apple LLVM 8.1.0 (clang-802.0.42)]

Is there a particular objectpath version for which this issue reproduces? or anything particular to your environment?

[timb07]

My original report was for Python 3.7.5 on Ubuntu 18.04. I've just reproduced the issue on macOS 10.14.4 with Python 3.7.3, following the same steps as originally given.

More details:

$ pylint --version
pylint 2.4.4
astroid 2.3.3
Python 3.7.3 (default, Mar 31 2019, 02:12:56)
[Clang 10.0.1 (clang-1001.0.46.3)]

$ pip freeze
astroid==2.3.3
isort==4.3.21
lazy-object-proxy==1.4.3
mccabe==0.6.1
objectpath==0.6.1
pylint==2.4.4
six==1.13.0
typed-ast==1.4.0
wrapt==1.11.2

And I've just reproduced it with Python 3.8.0 as well:

$ pylint --version
pylint 2.4.4
astroid 2.3.3
Python 3.8.0 (default, Nov 27 2019, 20:35:55)
[Clang 10.0.1 (clang-1001.0.46.3)]

And I've also confirmed that the problem doesn't exist with Python 3.6.9 (again on macOS this time).