Hi Paul,
disclaimer: I didn't try to install Cantera. But generally, to install
Python packages that are not part of the SageMath ecosystem, you should
first open a Sage shell by the command
sage -sh
Then, in the Sage shell, you follow the instructions to install the
package. Sage has its own Python, that is separate from
your system-wide Python. So, if you follow the instruction in a plain
terminal, the installation will end in the system-wide Python that
SageMath can not find.
Example from my machine:
System-wide Python:
king@king-ThinkPad-T430:~$ python --version
Python 2.7.12
Sage's Python
king@king-ThinkPad-T430:~$ ~/Sage/git/sage/sage -sh
...
Note: SAGE_ROOT=/home/king/Sage/git/sage
(sage-sh) king@king-ThinkPad-T430:~$ python --version
Python 2.7.13
Best regards,
Simon