#20437: Misinstallation of Python in Cygwin
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Reporter: embray | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-7.2
Component: porting: Cygwin | Resolution:
Keywords: | Merged in:
Authors: Erik Bray | Reviewers:
Report Upstream: Reported | Work issues:
upstream. No feedback yet. | Commit:
Branch: u/embray/cygwin- | 71062f01ef52e723f780044ffd08b4f46520bd75
python-install | Stopgaps:
Dependencies: |
-------------------------------------+-------------------------------------
Changes (by embray):
* status: needs_work => needs_review
* upstream: Not yet reported upstream; Will do shortly. => Reported
upstream. No feedback yet.
Old description:
> I've encountered yet another problem in my quest to get sage building on
> Cygwin. I'm surprised this hasn't come up before though which makes me
> wonder if I'm doing something wrong.
>
> The DLL loader library, libpython2.7.dll.a, gets installed to
> `$(SAGE_LOCAL)/lib/python2.7/config/` which is not normally on the ld
> search path (similar on Python 3 I think).
>
> This means that when building extension modules `-lpython2.7` is actually
> linking against my system Python (in this case the Python that came with
> cygwin--also Python 2.7.10). This is of course wrong, but isn't a
> problem for the majority of modules, including sage itself (at least it
> wasn't a problem for compiling). It was actually PIL(low) where this
> fell apart because it used some `PyUnicode_` functions that were not
> found in my system libpython because it was compiled with `--enable-
> unicode=ucs2`, whereas Sage builds Python with `--enable-unicode=ucs4`.
>
> When installing Python, Sage should be making a symlink to
> `$(SAGE_LOCAL)/lib/python2.7/config/libpython2.7.dll.a` in
> `$(SAGE_LOCAL)/lib`.
>
> I'm leaning toward calling this an upstream bug--I don't understand why
> this isn't done automatically by Python's Makefile. The relevant portion
> begins [https://hg.python.org/cpython/file/v2.7.10/Makefile.pre.in#l916
> here]. It seems that if a DLL is built it ''does not'' install a symlink
> to the loader library in lib/.
>
> For reference, Cygwin's own system package for Python installs this
> symlink manually...
New description:
I've encountered yet another problem in my quest to get sage building on
Cygwin. I'm surprised this hasn't come up before though which makes me
wonder if I'm doing something wrong.
The DLL loader library, libpython2.7.dll.a, gets installed to
`$(SAGE_LOCAL)/lib/python2.7/config/` which is not normally on the ld
search path (similar on Python 3 I think).
This means that when building extension modules `-lpython2.7` is actually
linking against my system Python (in this case the Python that came with
cygwin--also Python 2.7.10). This is of course wrong, but isn't a problem
for the majority of modules, including sage itself (at least it wasn't a
problem for compiling). It was actually PIL(low) where this fell apart
because it used some `PyUnicode_` functions that were not found in my
system libpython because it was compiled with `--enable-unicode=ucs2`,
whereas Sage builds Python with `--enable-unicode=ucs4`.
When installing Python, Sage should be making a symlink to
`$(SAGE_LOCAL)/lib/python2.7/config/libpython2.7.dll.a` in
`$(SAGE_LOCAL)/lib`.
I'm leaning toward calling this an upstream bug--I don't understand why
this isn't done automatically by Python's Makefile. The relevant portion
begins [https://hg.python.org/cpython/file/v2.7.10/Makefile.pre.in#l916
here]. It seems that if a DLL is built it ''does not'' install a symlink
to the loader library in lib/. I've brought this up here:
https://mail.python.org/pipermail/python-dev/2016-April/144315.html
For reference, Cygwin's own system package for Python installs this
symlink manually... It seems odd not to do it by default.
--
--
Ticket URL: <http://trac.sagemath.org/ticket/20437#comment:12>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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