Is there any way to make Python play well with stow?

Discussion in 'Python' started by Tim Bradshaw, Jun 1, 2004.

  1. Tim Bradshaw

    Tim Bradshaw Guest

    I'd like to be able to install python with stow, and then to install
    various modules which use distutils, also with stow. This currently
    pretty much won't work, because Python chases symlinks to set
    sys.prefix, which means that the site path gets set to the `true'
    location rather than the one with all the links. This means that
    Python won't find modules you install with stow, unless you glue the
    linky site directory into sys.path. Doing this is OK for
    applications, but it means that things like distutils break if there
    are modules which depend on other modules which you've installed,
    because it won't find those modules.

    As an example, assume I have things appear in /local/ and the stow dir
    is /local/packages/. So I build python with:

    $ ./configure --prefix=/local
    $ make
    $ make install prefix=/local/packages/python-2.3.4

    Then stow it:

    $ (cd /local/packages; stow python-2.3.4)

    This python's sys.path will have /local/packages in it since
    sys.prefix &co have that.

    Now install a module, say Numeric:

    $ python setup.py install --prefix=/local/packages/numeric
    $ (cd /local/packages; stow numeric)

    At this point stow will have set things up so that
    /local/lib/python-2.3/site-packages/ is a directory (not a link) which
    contains links such as Numeric and Numeric.pth pointing to the
    appropriate places under /local/packages/numeric/.

    Unfortunately python will never even look for this site-packages dir
    because of the link-following in the computation of sys.prefix: it
    only considers /local/packages/python-2.3.4/lib/python2.3/site-packages/.
    So any other module I try and install which needs Numeric will fail.

    I can fix this by adding a .pth file to the `real' site packages dir
    which points at the linky one, but this is something extra to do every
    time I install Python: I'd really like to be able to keep the python
    directory tree completely clean.

    Is there anything else I can do that's not essentially equivalent to
    this (so, for instance, not making the real site-packages dir be a
    symlink back to the linky one...)?

    I think it would be a good thing if the computation of sys.prefix did
    the following: if the python binary is a symbolic link, then before
    chasing the symlink, still look for things `this side' of it. If you
    find something that looks like a python installation, then construct
    sys.prefix &c using those paths. Only if that fails should you chase
    the link and look for an installation on the far side of it. This
    would allow things like stow to work transparently, I think. Of
    course there may be disadvantages of doing this which I haven't
    thought of.

    Thanks

    --tim
     
    Tim Bradshaw, Jun 1, 2004
    #1
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  2. Tim Bradshaw

    Tim Bradshaw Guest

    (Tim Bradshaw) wrote in message news:<>...
    > I'd like to be able to install python with stow, and then to install
    > various modules which use distutils, also with stow. This currently
    > pretty much won't work, because Python chases symlinks to set
    > sys.prefix, which means that the site path gets set to the `true'
    > location rather than the one with all the links. This means that
    > Python won't find modules you install with stow, unless you glue the
    > linky site directory into sys.path. Doing this is OK for
    > applications, but it means that things like distutils break if there
    > are modules which depend on other modules which you've installed,
    > because it won't find those modules.


    > [and so on]


    About 5 minutes after posting this I discovered PYTHONHOME, which
    completely stops all the intuiting sys.prefix stuff. I feel like a
    fool now, and more so since posting via google means I couldn't even
    point out my idiocy until today.

    --tim
     
    Tim Bradshaw, Jun 2, 2004
    #2
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