proper polymake preferences, perhaps using Python 'with'

[mkoeppe]

Following up on #22452 (Create a Polymake pexpect interface):

Polymake's prefer is bad because it is too persistent, writing to a preference file. We cannot use prefer_now directly because it is local to the current line. We should have a way to set preferences local to a code block. Perhaps a Python context manager (using the with keyword) would be the right solution.

See also: #22710: Meta-ticket: polymake

[SimonKing]

Replying to mkoeppe:

Polymake's prefer is bad because it is too persistent, writing to a preference file. We cannot use prefer_now directly because it is local to the current line. We should have a way to set preferences local to a code block. Perhaps a Python context manager (using the with keyword) would be the right solution.

I agree that we don't want Sage to set preferences permanently (unless the user asks it). Although a "with" block may be a good solution for modules, I don't think that we want that in an interactive session.

So, I think ideally we would have a method polymake.preferences, so that

sage: polymake.preferences(...)

would set preferences that expire when the sage session ends, and

with polymake.preferences(...):
    many
    lines
    of
    code

would set preferences that expire when the "with" block ends.