'from .foo import *' introduces 'foo' as symbol that mypy doesn't recognise

[Wilfred]

The typeshed definition for yaml/__init__.pyi contains the following (src):

from yaml.error import *

This has two side effects: it adds every symbol foo in yaml/error.py as yaml.foo. However, it also defines yaml.error.

I believe this is why the mypy complains about the following correct code:

import yaml

def foo():
    # type: () -> None
    yaml.error

$ mypy --py2 foo.py
foo.py:5: error: Module has no attribute "error"

Oddly, I can't reproduce this on Python 3. The following code does not produce a type error:

import yaml

def foo() -> None:
    yaml.error

[gvanrossum]

I cannot repro this at all. What mypy version are you using? What's in your mypy.ini?

[Wilfred]

I can reproduce this on both mypy 0.530 and 0.540. I don't have a mypy.ini.

$ cat example.py
import yaml

def foo():
    # type: () -> None
    yaml.error
$ mypy --py2 example.py
example.py:5: error: Module has no attribute "error"

[gvanrossum]

I still can't repro it. I wonder... Do you have a file named yaml.py in your current directory or in your $PYTHONPATH?

[Wilfred]

Nope, empty directory and PYTHONPATH isn't set.

$ ls -a
./  ../  example.py

$ cat example.py
import yaml

def foo():
    # type: () -> None
    yaml.error

$ mypy --py2 example.py
example.py:5: error: Module has no attribute "error"

$ echo $PYTHONPATH

$ mypy --version
mypy 0.540

I'm using mypy in a Conda environment on OS X. I don't have yaml or pyyaml installed in that environment.

Interestingly, I can't reproduce this with pyvenv:

$ python3.6 -m venv myenv
$ source ./myenv/bin/activate

$ pip install mypy
Collecting mypy
  Using cached mypy-0.540-py3-none-any.whl
Collecting typed-ast<1.2.0,>=1.1.0 (from mypy)
  Using cached typed_ast-1.1.0-cp36-cp36m-macosx_10_11_x86_64.whl
Installing collected packages: typed-ast, mypy
Successfully installed mypy-0.540 typed-ast-1.1.0

$ mypy --py2 example.py

[ilevkivskyi]

Then it means this is a broken installation with old typeshed, try installing with --no-cache or similar, see #3768

[gvanrossum]

@Wilfred If Ivan's suggestion works, I would love to understand how your system got into this state (and what exactly that state was -- seems an old typeshed is taking precedence over the correct one). Perhaps before deleting anything could you run mypy -v -2 example.py for me? That should show where the yaml.pyi file lives. Then can you confirm that the various import * line in its __init__.py are commented out? See python/typeshed#1439.

[Wilfred]

Running mypy with -v:

$ mypy -v -2 example.py
LOG:  Mypy version 0.540
LOG:  Metadata not found for example
LOG:  Parsing example.py (example)
LOG:  Metadata not found for yaml
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2/yaml/__init__.pyi (yaml)
LOG:  Metadata not found for builtins
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/__builtin__.pyi (builtins)
LOG:  Metadata not found for typing
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/typing.pyi (typing)
LOG:  Metadata not found for abc
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/abc.pyi (abc)
LOG:  Metadata not found for mypy_extensions
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2and3/mypy_extensions.pyi (mypy_extensions)
LOG:  Metadata not found for types
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/types.pyi (types)
LOG:  Metadata not found for collections
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/collections.pyi (collections)
LOG:  Metadata not found for _weakrefset
LOG:  Parsing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/_weakrefset.pyi (_weakrefset)
LOG:  Loaded graph with 9 nodes
LOG:  Found 3 SCCs; largest has 7 nodes
LOG:  Processing SCC of size 7 (types mypy_extensions abc typing _weakrefset collections builtins) as inherently stale
LOG:  Writing types /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/types.pyi .mypy_cache/2.7/types.meta.json .mypy_cache/2.7/types.data.json
LOG:  Cached module types has changed interface
LOG:  Writing mypy_extensions /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2and3/mypy_extensions.pyi .mypy_cache/2.7/mypy_extensions.meta.json .mypy_cache/2.7/mypy_extensions.data.json
LOG:  Cached module mypy_extensions has changed interface
LOG:  Writing abc /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/abc.pyi .mypy_cache/2.7/abc.meta.json .mypy_cache/2.7/abc.data.json
LOG:  Cached module abc has changed interface
LOG:  Writing typing /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/typing.pyi .mypy_cache/2.7/typing.meta.json .mypy_cache/2.7/typing.data.json
LOG:  Cached module typing has changed interface
LOG:  Writing _weakrefset /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/_weakrefset.pyi .mypy_cache/2.7/_weakrefset.meta.json .mypy_cache/2.7/_weakrefset.data.json
LOG:  Cached module _weakrefset has changed interface
LOG:  Writing collections /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/collections.pyi .mypy_cache/2.7/collections.meta.json .mypy_cache/2.7/collections.data.json
LOG:  Cached module collections has changed interface
LOG:  Writing builtins /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/stdlib/2/__builtin__.pyi .mypy_cache/2.7/builtins.meta.json .mypy_cache/2.7/builtins.data.json
LOG:  Cached module builtins has changed interface
LOG:  Processing SCC singleton (yaml) as inherently stale with stale deps (builtins typing)
LOG:  Writing yaml /Users/whughes/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2/yaml/__init__.pyi .mypy_cache/2.7/yaml/__init__.meta.json .mypy_cache/2.7/yaml/__init__.data.json
LOG:  Cached module yaml has changed interface
LOG:  Processing SCC singleton (example) as inherently stale with stale deps (builtins yaml)
LOG:  Deleting example /Users/whughes/tmp/example.py .mypy_cache/2.7/example.meta.json .mypy_cache/2.7/example.data.json
LOG:  No fresh SCCs left in queue
LOG:  Build finished in 0.517 seconds with 9 modules, 1385 types, and 1 errors
example.py:5: error: Module has no attribute "error"

[Wilfred]

This rather looks like it's using a copy of typeshed from inside mypy itself. Are there any other tests you'd like me to run?

[Wilfred]

The typeshed inside my conda env does indeed have yaml/error.pyi:

~/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2and3/yaml
$ ls
__init__.pyi  constructor.pyi  emitter.pyi  events.pyi  nodes.pyi   reader.pyi       resolver.pyi  serializer.pyi
composer.pyi  dumper.pyi       error.pyi    loader.pyi  parser.pyi  representer.pyi  scanner.pyi   tokens.pyi

~/miniconda2/envs/scratch3/lib/mypy/typeshed/third_party/2/yaml
$ ls
__init__.pyi  constructor.pyi  emitter.pyi  events.pyi  nodes.pyi   reader.pyi       resolver.pyi  serializer.pyi
composer.pyi  dumper.pyi       error.pyi    loader.pyi  parser.pyi  representer.pyi  scanner.pyi   tokens.pyi

I've also confirmed that creating a fresh conda env does not reproduce this issue.

[gvanrossum]

So does Ivan's suggestion solve your problem or not?

The key bit of information is whether yaml/init.pyi contains a from errors import * that's not commented-out. In older typeshed versions it was commented out -- uncommenting it caused the error object to appear upon mere import of yaml. (Emulating the behavior of yaml at runtime.)

If you really can't fix this problem in your environment, a workaround is to add import yaml.error to your code. That should work in all environments.

[Wilfred]

I'm not sure how my conda environment got into this state, so I'm going to close this. If I encounter it again, I'll reopen with reproduction steps.

I'm happily using mypy in other virtualenvs/conda environments.