python3Packages.dotnetcore2: init at 2.1.8.1

[jonringer]

Motivation for this change

Upstreaming this from an expression I use at work

why someone felt like packaging this instead of telling users to install it... idk

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Notify maintainers

cc

includes dotnet-sdk closure, i will try to reduce the size of that package

$ nix path-info -Sh ./result
/nix/store/jxld4i96bfdk76ic904vkvczr50jpq2d-python3.7-dotnetcore2-2.1.8.1        834.4M

$ tree ./result/
./result/
├── lib
│   └── python3.7
│       └── site-packages
│           ├── dotnetcore2
│           │   ├── __init__.py
│           │   └── runtime.py
│           └── dotnetcore2-2.1.8.1.dist-info
│               ├── LICENSE.txt
│               ├── METADATA
│               ├── RECORD
│               ├── top_level.txt
│               └── WHEEL
└── nix-support
    └── propagated-build-inputs

[1 built, 0.0 MiB DL]
https://github.com/NixOS/nixpkgs/pull/67787
1 package were build:
python37Packages.dotnetcore2

[jonringer]

@marsam @mmahut do you mind taking a look at this? I'm using this at work and seems to work fine.