nixpkgs python repl isn't very terminal-friendly

[copumpkin]

Issue description

I can't use standard terminal keys in the python from nixpkgs.

Steps to reproduce

1. nix-shell -p python
2. python
3. Enter 5 + 5
4. Press the up arrow.
5. Weep when you see ^[[A
6. Press the left arrow
7. Weep when you see ^[[D
8. Press ctrl-A
9. Weep when you see ^A

Technical details

I tried it on darwin nixpkgs and on NixOS:

• NixOS version: 16.03pre73316.93d8671 (Emu)
• Darwin Nixpkgs version: 16.09pre87549.8a1e7cd

[rvl]

Readline is available if you use nix-shell -p pythonFull.

Do you mean that the default python attribute should be changed, and/or documentation added?

[copumpkin]

Yeah, perhaps my issue is just using the default python. Note that this also affects transitive dependencies, so if I do nix-shell -p pythonPackages.boto3 the python I get in there will also be unfriendly.

It's also kind of awkward to have the distinction, because if I do nix-shell -p pythonPackages.boto3 pythonFull I end up with no readline, but nix-shell -p pythonFull pythonPackages.boto3 gives me a version with readline.

I don't know why the default attribute is the weaker version, and I don't necessarily want to replace it by pythonFull, but I do want the overall default experience to be good for people coming from other systems. As it stands, it seems like making readline optional adds some confusion.

[FRidh]

By default python is a stripped version. All packages that use buildPythonPackage also depend on this version.

It's also kind of awkward to have the distinction, because if I do nix-shell -p pythonPackages.boto3 pythonFull I end up with no readline, but nix-shell -p pythonFull pythonPackages.boto3 gives me a version with readline.

I guess the setupHook together with PYTHONPATH being evaluated from left to right is responsible for that.

I do want the overall default experience to be good for people coming from other systems

Do we want python to refer to a full version of Python by default, or do we want to point it to something that is sufficient for most users and especially sufficient for most other packages that depend on Python, and taking into account the closure size?

[domenkozar]

We should include readline by default. I've been long wanting to do that, but never had the time.

[copumpkin]

@domenkozar what's the downside? All python packages gain a slightly smaller runtime closure?

[domenkozar]

I think we'll survive:

$ du -sh $(nix-build -A readline.all)
752K    /nix/store/q97il2whcmnmcyvr62n252f1ay5i4irq-readline-6.3p08
168K    /nix/store/mbsx71lzniqhhv4fi7al50aavqmqq4a9-readline-6.3p08-dev
888K    /nix/store/2aj8lx78bfnmhmbjvh34f0amqnfibbaq-readline-6.3p08-doc

[copumpkin]

😱

[FRidh]

Fixes with #19309.