fix: make python setup.py works for development mode

[megazone87]

namely, install by bellow cmds works:
python setup.py develop or pip install -e .

[csukuangfj]

Thanks for the contribution.

setup.py is mainly used to build wheels that can be installed by normal users.

As developers, I would recommend you to read https://k2-fsa.github.io/k2/installation/for_developers.html, which does not use setup.py at all.

[megazone87]

Yeah, I read that doc. But python develop mode is a common routine for developers, e.g. it requires nothing to do after you change python sources. And if c++ sources change, just pip install -e ., instead of firstly make and others. And u don't need an env shell to source.

[danpovey]

I think it would be nice if setup.py were to support development mode, but I don't understand how this change accomplishes that. Is the empty string supposed to be a key for that package_dir arg? I'd like to understand what is going on.

[megazone87]

I think it would be nice if setup.py were to support development mode, but I don't understand how this change accomplishes that. Is the empty string supposed to be a key for that package_dir arg? I'd like to understand what is going on.

I think the old code should work,
according to https://docs.python.org/3/distutils/setupscript.html#listing-whole-packages

But not, I think there's a bug of setuptool pkg, and make a PR: pypa/setuptools#2803.

And we could wait for their answers, it's not critical for us anyway.