Exception while typechecking: KeyError: 'typing'

[corydolphin]

Hello,

First, thank you all for your work on MyPy, adding static typing to Python is a huge boon.

MyPy is hitting an exception while typechecking our project, both with version 0.720 and with master 0.730+dev.8954045912e8d7f00af5d7d6289085dd8eb8c64a on Python 3.6.5

The minimal test case which triggers the exception is:

import contextlib


@contextlib.contextmanager
def do_nothing(*args, **kwargs):
    yield

When evaluated with a config file which contains follow_imports_for_stubs = True, as well as passing --follow-imports=skip in the commandline. Are these two incompatible? Their names almost suggest as much.

E.g.

[mypy]
follow_imports_for_stubs = True

python -m mypy --show-traceback --follow-imports=skip --config-file=example.cfg example.py
example.py:4: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.730+dev.8954045912e8d7f00af5d7d6289085dd8eb8c64a
Traceback (most recent call last):
  File "/var/lib/conda/envs/py35/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/var/lib/conda/envs/py35/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/__main__.py", line 12, in <module>
    main(None, sys.stdout, sys.stderr)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/main.py", line 83, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 163, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 225, in _build
    graph = dispatch(sources, manager, stdout)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 2562, in dispatch
    process_graph(graph, manager)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 2871, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 2970, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/build.py", line 2066, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 291, in check_first_pass
    self.accept(d)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 402, in accept
    stmt.accept(self)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/nodes.py", line 756, in accept
    return visitor.visit_decorator(self)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 3294, in visit_decorator
    self.check_func_item(e.func, name=e.func.name())
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 788, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 862, in check_func_def
    if not self.is_generator_return_type(typ.ret_type, defn.is_coroutine):
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 611, in is_generator_return_type
    gt = self.named_generic_type('typing.Generator', [any_type, any_type, any_type])
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 3843, in named_generic_type
    info = self.lookup_typeinfo(name)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 3849, in lookup_typeinfo
    sym = self.lookup_qualified(fullname)
  File "/var/lib/conda/envs/py35/lib/python3.6/site-packages/mypy/checker.py", line 3897, in lookup_qualified
    n = self.modules[parts[0]]
KeyError: 'typing'
example.py:4: : note: use --pdb to drop into pdb

[JukkaL]

Here is a smaller example that will crash:

def f():
    yield

It looks like follow_imports_for_stubs = True and --follow-imports=skip don't work together at the moment. They cause the stub for typing to be skipped, which will break almost everything. I don't see why they couldn't work together, though.

[97littleleaf11]

This issue can be closed.

[corydolphin]

Thank you both! Closed.