It's relatively easy using import system hooks in Python to make new file types 'importable' using the standard import statement. E.g. a file like mymodule.sage could be imported as mymodule just as though it were mymodule.py.

Importing a .sage module is of course just a thin layer over a normal Python module import, but to pass it through the Sage preparser.

There are of course some risks to making .sage modules importable. For example, what if a user has both a foo.sage and an foo.py? Which one takes priority upon import foo? In particular it could introduce quite some surprises if a user has something like os.sage in their current directory.

Unfortunately it's not possible to extend the syntax of import statements, which would be nice. But, while the "module name" portion of an import statement must be a valid identifier, we can still otherwise process it however we want. So maybe .sage module imports would be initiated only if .sage is used explicitly in the import statement. So for example, to import a sage module named foo.sage one would literally write:

import foo.sage

to distinguish it from a Python module named foo.py. Of course, if there is a Python package named foo that happens to have a sage sub-module there is still a conflict. But this is a bit unlikely for most cases.

So in order to make such a feature available, while mitigating potential problems with it, I might suggest a few additional restrictions:

1. There would be a function to enable/disable .sage import functionality on the fly. When first introduced this would be disabled by default, but we would certainly want to make the feature easily discoverable through the documentation, with all the caveats discussed.

2. In the off chance that there is a conflict between a .sage module an a plain Python module, the system should check for that. In that case the .sage module still takes priority (if .sage imports are enabled), but a warning about the conflict is shown.

3. This feature should be Python 3 only. That will make it easier to implement, due to the significant differences between the import systems, and it will also give a nice motivation, to anyone who wants the feature, to switch to Python 3.

See also: https://groups.google.com/d/msg/sage-devel/tL8Whabyaoc/RMzlMyUtBwAJ

CC: @dimpase @jdemeyer @EmmanuelCharpentier @nthiery @nbruin @yuan-zhou

Component: interfaces

Issue created by migration from https://trac.sagemath.org/ticket/27074