[with patch, positive review] ideal([]) gives unhelpful error message

[broune]

When I type "ideal([])" in Sage 4.0.1 I get an error message intended for a different case:

sage: ideal([])
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
...
TypeError: unable to find common ring into which all ideal generators map

This error message is incorrect since, trivially, the empty set of generators will map into any ring at all. The attached patch changes this to

sage: ideal([])
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
...
ValueError: unable to determine which ring to embed the ideal in

By the way, the function ideal in ideal.py has a documentation section named TESTS with doctests in it. As far as I can determine, these doctests do not get run.

[jhpalmieri]

By the way, the function ideal in ideal.py has a documentation section named TESTS with doctests in it. As far as I can determine, these doctests do not get run.

I'm not sure why you say this. If you add lines like

sage: 3+5
9

to that section, you get a doctest failure. At least, I do. I think that your addition to that section doesn't produce an error because it starts with Sage:, not sage:. Since you already test this failure earlier, I'm adding a referee's patch deleting this non-doctest from the TESTS section, and also fixing a small reST issue.