$ pacman -Syyuw
...
resolving dependencies...
error: failed to prepare transaction (could not satisfy dependencies)
:: mypaint: installing python2-protobuf (3.0.2-2) breaks dependency 'protobuf-python'

$ pacman -Si mypaint python2-protobuf protobuf-python
Repository      : community
Name            : mypaint
Version         : 1.2.0-3
Description     : A fast and easy painting application for digital painters, with brush dynamics
Architecture    : i686
URL             : http://mypaint.org/
Licenses        : GPL  LGPL
Groups          : None
Provides        : None
Depends On      : pygtk  python2-numpy  protobuf-python  python2  json-c  lcms2  python2-gobject  gtk3
Optional Deps   : None
Conflicts With  : None
Replaces        : None
Download Size   : 32.57 MiB
Installed Size  : 39.06 MiB
Packager        : Sergej Pupykin <pupykin.s+arch@gmail.com>
Build Date      : Wed 27 Apr 2016 04:13:17 PM EDT
Validated By    : MD5 Sum  SHA-256 Sum  Signature

Repository      : testing
Name            : python2-protobuf
Version         : 3.0.2-2
Description     : Python 2 bindings for Google Protocol Buffers
Architecture    : i686
URL             : https://developers.google.com/protocol-buffers/
Licenses        : BSD
Groups          : None
Provides        : python2-protobuf
Depends On      : python2  python2-six  protobuf=3.0.2
Optional Deps   : None
Conflicts With  : python2-protobuf
Replaces        : None
Download Size   : 376.77 KiB
Installed Size  : 3065.00 KiB
Packager        : Bartlomiej Piotrowski <bpiotrowski@archlinux.org>
Build Date      : Fri 11 Nov 2016 03:34:41 PM EST
Validated By    : MD5 Sum  SHA-256 Sum  Signature

Repository      : extra
Name            : python2-protobuf
Version         : 2.6.1-2
Description     : Python 2 bindings for Google Protocol Buffers
Architecture    : i686
URL             : https://developers.google.com/protocol-buffers/
Licenses        : BSD
Groups          : None
Provides        : protobuf-python
Depends On      : python2  protobuf=2.6.1
Optional Deps   : None
Conflicts With  : protobuf-python
Replaces        : protobuf-python
Download Size   : 114.24 KiB
Installed Size  : 765.00 KiB
Packager        : Allan McRae <allan@archlinux.org>
Build Date      : Sat 05 Dec 2015 12:21:51 PM EST
Validated By    : MD5 Sum  SHA-256 Sum  Signature

error: package 'protobuf-python' was not found