Bug Report

When mypy is run multiple times on a Python module containing from aws_cdk import core it will fail every 2nd time due to the error "Skipping analyzing 'aws_cdk': found module but no type hints or library stubs".

Disabling the mypy cache with --no-incremental will result in mypy passing every time.

To Reproduce

1. Install mypy and aws-cdk.core.
2. Create a Python module with from aws_cdk import core.
3. Run mypy on the module and it will pass.
4. Run mypy on the module again and it will fail. Subsequent runs will cycle between passing and failing.

$ python3.8 -m venv .venv && source .venv/bin/activate
(.venv) $ pip install mypy==0.790 aws-cdk.core==1.80.0
(.venv) $ echo 'from aws_cdk import core' > repro.py
(.venv) $ mypy repro.py
Success: no issues found in 1 source file
(.venv) $ mypy repro.py
repro.py:1: error: Skipping analyzing 'aws_cdk': found module but no type hints or library stubs
repro.py:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
Found 1 error in 1 file (checked 1 source file)
(.venv) $ mypy repro.py
Success: no issues found in 1 source file
(.venv) $ mypy repro.py
repro.py:1: error: Skipping analyzing 'aws_cdk': found module but no type hints or library stubs
repro.py:1: note: See https://mypy.readthedocs.io/en/latest/running_mypy.html#missing-imports
Found 1 error in 1 file (checked 1 source file)

Expected Behavior

Running mypy on a module containing only from aws_cdk import core should always pass.

Actual Behavior

Every second time mypy is run on the module it will report an error.

Your Environment

• Mypy version used: 0.790
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8.2
• Operating system and version: macOS
• aws-cdk.core version used: 1.80.0

The problem may be related to how the package that is installed is aws-cdk.core but the namespace being imported from is aws_cdk. A workaround is to change:

from aws_cdk import core

to:

import aws_cdk.core as core

The first form is what is generated by the cdk tool and used in the cdk example code.