cannot do --user install on homebrew

[glyph]

With today's get-pip.py (and with every other version of pip I tried):

$ /usr/local/bin/python get-pip.py --user 
Collecting pip
Installing collected packages: pip
  Exception:
  Traceback (most recent call last):
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/basecommand.py", line 246, in main
      status = self.run(options, args)
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/commands/install.py", line 352, in run
      root=options.root_path,
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/req/req_set.py", line 693, in install
      **kwargs
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/req/req_install.py", line 817, in install
      self.move_wheel_files(self.source_dir, root=root)
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/req/req_install.py", line 1018, in move_wheel_files
      isolated=self.isolated,
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/wheel.py", line 138, in move_wheel_files
      name, user=user, home=home, root=root, isolated=isolated
    File "/var/folders/wd/y0p85qd48xx992w8rkclf7mc8xdc8d/T/tmpE5mm75/pip.zip/pip/locations.py", line 236, in distutils_scheme
      i.finalize_options()
    File "/usr/local/lib/python2.7/site-packages/setuptools-12.0.5-py2.7.egg/setuptools/command/install.py", line 38, in finalize_options
      orig.install.finalize_options(self)
    File "/usr/local/Cellar/python/2.7.9/Frameworks/Python.framework/Versions/2.7/lib/python2.7/distutils/command/install.py", line 268, in finalize_options
      raise DistutilsOptionError("can't combine user with prefix, "
  DistutilsOptionError: can't combine user with prefix, exec_prefix/home, or install_(plat)base

For some reason, Pip thinks that every install into homebrew python (perhaps any python with a non-standard prefix?) is a --prefix install, and refuses to let me install anything as --user.

[rbtcollins]

FWIW I ran into a similar thing in a different context - with my cpython trunk build. There's some limitations in sysconfig that drive it, from memory.

[dstufft]

Homebrew sets a Python specific distutils.cfg that sets the --prefix option which distutils doesn't allow you to set at the same time as --user. I think that @tdsmith probably knows more about the specifics of why Homebrew does this and if there's anything pip can do to help.

[tdsmith]

Homebrew changes the default install prefix so that packages are installed to the HOMEBREW_PREFIX (i.e. /usr/local) prefix and not to python's private, version-specific prefix (i.e. /usr/local/Cellar/python/2.7.8_2).

There's a good argument that Homebrew's solution is morally incorrect but we try hard to avoid carrying patches that will never be merged upstream.

There's an annoying but documented workaround involving passing prefix= at install time, like this:

pip install --user --install-option="--prefix=" spam

Proposals so far for resolving this are https://bugs.python.org/issue22269 (allowing --user to trump --prefix in distutils option parsing instead of complaining about a conflict) and Homebrew/legacy-homebrew#31811 (patching dist.py). (These are actually the same solution; Homebrew is happy to carry a patch as soon as it's accepted upstream, without waiting for it to actually appear in a release.)

A possible workaround is for pip to always pass a null prefix to setup.py when --user is selected, as in our workaround.

[glyph]

@tdsmith - The --install-option workaround doesn't work with wheels. Since I love wheels and I obsessively build them for everything nowadays (allowing me, among other things, to actually get work done on airplanes, which I will be on 4 more of in the coming month), that means I can't use homebrew without virtualenv, and homebrew's virtualenv is out of date :).

Back to easy_install I guess? ;-)

[dstufft]

The --install-option work around would work if pip did it though.

[tdsmith]

Aside: I don't believe Homebrew packages virtualenv; I've rejected PRs for it before.

[tdsmith]

Thanks for flagging that our workaround doesn't work with wheels as is; I hadn't realized but I guess I should have.

[glyph]

@dstufft - are you suggesting that pip could always do --install-option=--prefix= when --user is specified? It seems like that might be the Right Thing to do.

[dstufft]

Yes.

[dstufft]

Closed by #2934