Error in display of a continuous map between open intervals

[tscrim]

Define a continuous map between two intervals:

sage: R.<t> = RealLine()
sage: I = R.open_interval(0, 2*pi)
sage: J = R.open_interval(2*pi, 6*pi)
sage: h = J.continuous_map(I, ((t-2*pi)/2,), name='h')

Before this ticket, it displays incorrectly:

sage: h.display()
h: (2*pi, 6*pi) --> (0, 2*pi)
   t |-->

After this ticket, it displays correctly:

sage: h.display()
h: (2*pi, 6*pi) --> (0, 2*pi)
   t |--> t = -pi + 1/2*t

[gh-mjungmath]

Removing the error block in starting in line 1069 in continuous_map.py then yields the following error:

sage: R.<t> = RealLine()
sage: I = R.open_interval(0, 2*pi)
sage: J = R.open_interval(2*pi, 6*pi)
sage: h = J.continuous_map(I, ((t-2*pi)/2,), name='h')
sage: h.display()
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-67d00ebd9395> in <module>()
      3 J = R.open_interval(Integer(2)*pi, Integer(6)*pi)
      4 h = J.continuous_map(I, ((t-Integer(2)*pi)/Integer(2),), name='h')
----> 5 h.display()

/home/michi/Projekte/sage-devel/local/lib/python3.7/site-packages/sage/manifolds/continuous_map.py in display(self, chart1, chart2)
   1113                 for ch1 in self._domain._top_charts:
   1114                     for ch2 in self._codomain.atlas():
-> 1115                         _display_expression(self, ch1, ch2, result)
   1116             else:
   1117                 for ch1 in self._domain._top_charts:

/home/michi/Projekte/sage-devel/local/lib/python3.7/site-packages/sage/manifolds/continuous_map.py in _display_expression(self, chart1, chart2, result)
   1086                 if len(expression) == 1:
   1087                     result._txt += repr(coords2[0]) + " = " + \
-> 1088                                   repr(expression[0]) + "\n"
   1089                     result._latex += latex(coords2[0]) + " = " + \
   1090                                     latex(coord_func[0]) + r"\\"

TypeError: 'sage.symbolic.expression.Expression' object is not subscriptable

Imho, this try-except block should be removed and replaced by another solution (or at least restricted to a smaller snippet of code) since it can mask bugs like these.

Furthermore, I just noticed that picewise defined continuous maps (not quite the unusal case) could not be displayed properly (cf. #28554 for scalar fields).

[gh-mjungmath]

Ah okay, it's the variable coords2. The bug can be fixed very quickly.

My other points still stand for discussion. :)

[gh-mjungmath]

New commits:

​2d3664b

Trac #30289: fix display for one variable

[tscrim]

Shouldn't the same change also be done for the result._latex?

Also, please add a doctest.

[gh-mjungmath]

Oh yes, sure. I was too impatient and haven't double checked. Sorry.

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​60040b5

Trac #30289: doctest + latex output

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​be7a363

Trac #30289: try-except shifted + code improvements

[gh-mjungmath]

This should be even better. I have shifted the try-except block. When an error is raised after this block, this must be a bug and therefore exposed as such.

[tscrim]

That is the danger of putting too much stuff into a try-except block. Thank you for the quick fix. LGTM.