Are you reporting a bug, or opening a feature request?
Bug report

Please insert below the code you are checking with mypy,
or a mock-up repro if the source is private. We would appreciate
if you try to simplify your case to a minimal repro.
This is not applicable to this bug report.

What is the actual behavior/output?
Running the mypy . command hangs forever after upgrading to MyPy 0.750 on macOS. Even trying mypy --version to verify the installed version hangs forever. Both commands have to be killed with Ctrl+C (pressing that multiple times is required, actually) after several minutes of waiting for output. Also tried uninstalling and re-installing MyPy from scratch with no luck. Only downgrading to 0.740 solves it from hanging forever, but now mypy --version takes about 45 seconds instead of < 1 second like it was before upgrading and downgrading, even though it outputs 0.740. Here is example output of killing mypy --version under 0.750 after several minutes:

$ mypy --version
^C^C^C^C^C^C^C^C^CTraceback (most recent call last):
  File "/Users/nwilliams/.virtualenvs/pysoa3/bin/mypy", line 6, in <module>
    from mypy.__main__ import console_entry
  File "/Users/nwilliams/.virtualenvs/pysoa3/lib/python3.7/site-packages/mypy/__main__.py", line 4, in <module>
    from mypy.main import main
  File "mypy/main.py", line 13, in <module>
  File "mypy/build.py", line 33, in <module>
  File "mypy/semanal.py", line 95, in <module>
  File "mypy/typeanal.py", line 30, in <module>
  File "<frozen importlib._bootstrap>", line 978, in _find_and_load
KeyboardInterrupt

What is the behavior/output you expect?
For mypy . to run in generally the same amount of time it took previously (~10-15 seconds) and for mypy --version to output and exit instantly, instead of hanging forever like they now do.

What are the versions of mypy and Python you are using?

$ python --version
Python 3.7.4
$ cat ~/.virtualenvs/pysoa3/lib/python3.7/site-packages/mypy/version.py 
__version__ = "0.750"

The Python version was installed from Homebrew.
Do you see the same issue after installing mypy from Git master?
If I pip install git+https://github.com/python/[email protected], mypy . works. That's the same version (0.750), just installed from Git instead of PyPi. So this appears to be an issue with the PyPi wheel.

What are the mypy flags you are using? (For example --strict-optional)

[mypy]
python_version = 3.7
check_untyped_defs = True
[mypy-tasks]
ignore_errors = True
[mypy-(several projects listed here).*]
ignore_missing_imports = True
...