setuptools/discussions/3288

app.py

def hello():
  print("hello")


__version__ = '0.1'

pyproject.toml

[build-system]
requires = ['setuptools>=42']
build-backend = 'setuptools.build_meta'

setup.cfg

[metadata]
name = app
# Commenting the line below, the package_dir fails the build
#     error: error in 'egg_base' option: '.*' does not exist or is not a directory
#
# Without commenting it, I get the ModuleNotFoundError I was getting earlier today
#      ModuleNotFoundError: app
version = attr: app.__version__
license = Proprietary
platforms = Linux

[options]
zip_safe = False
include_package_data = True
python_requires = >=3.8
install_requires =
package_dir =
    =.*