Public bug reported:
## Expected behavior:
Running `sage` after installing the `sagemath` command starts Sage, even
if `python3` resolves somewhere other than `/usr/bin/python3` (examples
of when it doesn't: virtual environments, use of the conda package
manager, pyenv)
## Actual behavior:
```
$ sage
Traceback (most recent call last):
File "/usr/share/sagemath/bin/sage-ipython", line 9, in
from sage.misc.banner import banner
ModuleNotFoundError: No module named 'sage'
```
## Reproduction:
```
$ sudo apt install sagemath
...
$ which python3
/usr/bin/python3
$ sage
┌┐
│ SageMath version 9.0, Release Date: 2020-01-01 │
│ Using Python 3.8.10. Type "help()" for help. │
└┘
sage: 1 + 1
2
sage:
Exiting Sage (CPU time 0m0.14s, Wall time 0m27.42s).
$ python3 -m venv --copies /tmp/testvenv # note: --copies is necessary for
full isolation
$ source activate /tmp/testvenv/bin/activate
$ which python3
/tmp/testvenv/bin/python3
$ sage
Traceback (most recent call last):
File "/usr/share/sagemath/bin/sage-ipython", line 9, in
from sage.misc.banner import banner
ModuleNotFoundError: No module named 'sage'
```
As a workaround for anybody else who stumbles into this, you can still
invoke sage as: `/usr/bin/python3 /usr/share/sagemath/bin/sage-ipython`,
which forces
## Additional information
There are a few layers of indirection at work in this bug, but at the
end of the day, this happens because of an `exec python3` embedded in
the part of the `sage` shell script responsible for launching Python.
Upstream reference:
https://github.com/sagemath/sage/blob/9.0/src/bin/sage#L614-L631
If I'm not mistaken, these lines should always point to /usr/bin/python3
for the Ubuntu package to avoid this flaw. Note that there are other
executables (ipython in particular) which may be appropriate to locate
against the system as well. The package maintainer(s) probably know how
to fix this better than I do, but I can confirm that replacing `exec
python3` with `exec /usr/bin/python3` in these two locations does appear
to resolve the problem.
## Boilerplate information:
1) system info
$ lsb_release -rd
Description:Ubuntu 20.04.3 LTS
Release:20.04
2) package info
$ apt-cache policy sagemath
sagemath:
Installed: 9.0-1ubuntu4
Candidate: 9.0-1ubuntu4
Version table:
*** 9.0-1ubuntu4 500
500 http://us.archive.ubuntu.com/ubuntu focal/universe amd64 Packages
100 /var/lib/dpkg/status
** Affects: sagemath (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1960459
Title:
Sage cannot be launched if `python3` does not point to system
interpreter
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