I am a developer of the Python package "snappy" which acquires extra
features when imported inside of Sage. Some of our Linux users have
recently reported difficulties with SnapPy on machines where Sage was
installed by the standard package manger making use of the system libraries
and in particular the system python. I have reproduced the problem on
Debian Sid but it also manifests itself on Fedora 28 [1]. The root of our
problem is that in this situation:
python -c "import sage.all"
results the error:
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/usr/lib/python2.7/dist-packages/sage/all.py", line 71, in <module>
from sage.env import SAGE_ROOT, SAGE_SRC, SAGE_DOC_SRC, SAGE_LOCAL,
DOT_SAGE, SAGE_ENV
File "/usr/lib/python2.7/dist-packages/sage/env.py", line 123, in <module>
_add_variable_or_fallback('SAGE_ETC', opj('$SAGE_LOCAL', 'etc'))
File "/usr/lib/python2.7/dist-packages/sage/env.py", line 103, in
_add_variable_or_fallback
value = sep.join(components)
TypeError: sequence item 0: expected string, NoneType found
whereas
sage -python -c "import sage.all"
works as expected. Currently, our Python package tests for whether it is
running in SageMath by:
_within_sage = False
try:
import sage.all
_within_sage = True
except ImportError:
pass
One solution for us (I think) would be to simply catch and ignore all types
of exceptions in the above block, but I was wondering if the current
behavior of 'python -c "import sage.all"' was expected or is this possibly
a bug? Or perhaps there is a work-around of some kind?
Thanks,
Nathan
P.S. In the Debian package "sage" does not accept the "-pip" flag, even
though installing the "sagemath" package does pull in "pip" (tested on a
clear Sid Docker container). Why is this? I ask because our current
instructions for installing SnapPy into SageMath use "sage -pip".
[1] See the second comment, not the original report, on
https://bitbucket.org/t3m/snappy/issues/14/
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