Type hints: PEP 561 compliance

[adamjstewart]

Although TorchGeo has type hints, mypy isn't actually able to find them. For example, if you pip install torchgeo, then run mypy on the following file:

from torchgeo.datasets import Sentinel2

ds = Sentinel2()

you'll see the following error:

$ mypy test.py 
test.py:1: error: Skipping analyzing "torchgeo.datasets": module is installed, but missing library stubs or py.typed marker
test.py:1: note: See https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
Found 1 error in 1 file (checked 1 source file)

It turns out that you have to explicitly tell mypy that your library has type hints by adding an empty py.typed file to the repo. You also need to tell setuptools to copy this file into both the sdist and wheel. See the following resources:

• PEP 561
• mypy error docs
• mypy PEP 561 docs