bpython depends on which

[memberbetty]

Issue description

File "/nix/store/80qva2zal82njkg4zvb7xg94mnikqksd-python3-3.6.8/lib/python3.6/subprocess.py", line 1364, in _execute_child
raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'which': 'which'

Steps to reproduce

Create a pure nix shell with python36Packages.bpython and execute bpython.

Technical details

18.09.

[dotlambda]

We should patch the call of which in https://github.com/bpython/bpython/blob/0.17.1-release/bpython/clipboard.py using substituteAll.
cc maintainer @flokli

[flokli]

@dotlambda it also tries to also call out to at least xclip (on Linux), pbcopy (on Darwin), and less - should we patch these in, too?

[dotlambda]

I don't think so as bpython shouldn't depend on X.

[memberbetty]

On Linux it should have xclip in its dependencies. Otherwise --pure is still going to fail.

The whole point of being able to run something via nix-shell --pure is that all dependencies are in, and if you have to know about random run-time dependencies that are not obvious, some advantages are nullified.

[dotlambda]

However, the whole point of bpython calling which is to make the dependency on xclip optional. It will hence not fail without it.

[memberbetty]

Fair point, but I prefer to have programs that are fully featured by default. People that run on limited platforms can make a more complicated expression optimized for their use cases.

[dotlambda]

@memberbetty If you do the PR, I won't reject patching in the path to xclip.

[stale]

Thank you for your contributions.

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[flokli]

I prefered not dragging in xclip and all its dependencies by default and opened #89439. On systems with xclip in $PATH, this should do the right thing - PTAL.