Python 3 dependency bloat

[edolstra]

The closure of the Python 3 package is much bigger than Python 2:

$ du -sch $(nix-store -qR $(nix-build -A python27))
110M    total

$ du -sch $(nix-store -qR $(nix-build -A python34))
269M    total

This is primarily due to the dependency on TCL/TK, which pulls in libX11 and other X11 libraries.

[domenkozar]

Yup. Python 2 has pythonFull with all modules, Python 3 has all modules builtin.

[edolstra]

Maybe we could have a python34Full equivalent to pythonFull? Or alternatively, put the tcl/tk stuff in a separate output. (Maybe the multiple-outputs branch already does that, @vcunat?)

[domenkozar]

I don't think separate output will help with Python modules, since nothing will reference it. It will essentially work the same way as current modules for Python 2.7 (as separate derivations) need to be specified explicitly.

[vcunat]

I think that's true. IIRC in that branch I was just fixing up the code to find python's dependencies.

[Profpatsch]

(triage) So do we need to change anything?

[vcunat]

Domen wrote it exactly, I believe. I think we shouldn't default to python3 before splitting it #18185.

[domenkozar]

New figures as of 16.09 are in #19255 (comment)

[domenkozar]

In staging due to #19309:

$ du -sch $(nix-store -qR $(nix-build -A python27))
22M     /nix/store/23vndix3mzcyw84kag06h8fh464g32nq-glibc-2.24
3.4M    /nix/store/4vq58j5cdpwpxmw2272kp3g9l9g8h71v-openssl-1.0.2j
100K    /nix/store/bjcyhbv746jklqb34k0sl34vkgz9n2r5-attr-2.4.47
108K    /nix/store/caz03y58cyrqn4i5ckdw4i21g9sdjb18-zlib-1.2.8
584K    /nix/store/cx5q5z8gpvlw323ycrsdbml8b2sq1dc4-gdbm-1.12
12M     /nix/store/p4zgz3jkfkm5rd48d7mwn9x8gjrz04nv-ncurses-6.0
400K    /nix/store/d2ycd6zq2rnzxbwwhspp5hvylv3b6qvp-readline-6.3p08
140K    /nix/store/n4772agrh2d5zhdr4902410zyqwj9ln4-acl-2.2.52
11M     /nix/store/ip4rh8n3p6ajnnf584wm2qj2x3ak73i8-coreutils-8.25
84K     /nix/store/iqp3bknzw3m3m8fbcwvgkjz6gra28pln-bzip2-1.0.6.0.1
4.8M    /nix/store/kdi9rs18zcpkx62wxxcn4m4km7dq38mj-gcc-5.4.0-lib
4.4M    /nix/store/nl0j7zjk555f38aw9jvh4hbxc2pnd8j8-db-5.3.28
952K    /nix/store/s7xrn3w9kadm3azl1yxws0bcq2azn7ns-sqlite-3.14.1
828K    /nix/store/vjm2a2zviphmxiz7j1ghl2dcw6f401bl-bash-4.3-p46
51M     /nix/store/qsi6jakmkl4cgdzn61svjlw2lfvj08mh-python-2.7.12
110M    total

$ du -sch $(nix-store -qR $(nix-build -A python35))
22M     /nix/store/23vndix3mzcyw84kag06h8fh464g32nq-glibc-2.24
3.4M    /nix/store/4vq58j5cdpwpxmw2272kp3g9l9g8h71v-openssl-1.0.2j
100K    /nix/store/bjcyhbv746jklqb34k0sl34vkgz9n2r5-attr-2.4.47
344K    /nix/store/c0np5q077pj2h0zd780c6yxmyzrryf3x-xz-5.2.2
108K    /nix/store/caz03y58cyrqn4i5ckdw4i21g9sdjb18-zlib-1.2.8
584K    /nix/store/cx5q5z8gpvlw323ycrsdbml8b2sq1dc4-gdbm-1.12
12M     /nix/store/p4zgz3jkfkm5rd48d7mwn9x8gjrz04nv-ncurses-6.0
400K    /nix/store/d2ycd6zq2rnzxbwwhspp5hvylv3b6qvp-readline-6.3p08
140K    /nix/store/n4772agrh2d5zhdr4902410zyqwj9ln4-acl-2.2.52
11M     /nix/store/ip4rh8n3p6ajnnf584wm2qj2x3ak73i8-coreutils-8.25
84K     /nix/store/iqp3bknzw3m3m8fbcwvgkjz6gra28pln-bzip2-1.0.6.0.1
952K    /nix/store/s7xrn3w9kadm3azl1yxws0bcq2azn7ns-sqlite-3.14.1
828K    /nix/store/vjm2a2zviphmxiz7j1ghl2dcw6f401bl-bash-4.3-p46
72M     /nix/store/x1yi7hz7xgqf0kgda5dzaywrmf85yc06-python3-3.5.2
123M    total

Python3 $PREFIX/lib itself grew by 20MB, so not much we can do about that.