Raise an error if matplotlib and latex are not installed when trying to render a png

[moorepants]

If you enable printing in qtconsole or ipython notebook and you have neither matplotlib or latex (or mathjax) installed you'll get empty pngs, e.g.:

from IPython.lib.latextools import latex_to_png doesn't seem to raise and error if neither are available.

[moorepants]

Maybe this should be: print using string or pretty printing if they are not installed.

[jksuom]

notebook: Newer versions of notebook load MathJax from the net. It does not matter if neither matplotlib nor latex is available. It will suffice to provide IPython with a latex representation of the output.

qtconsole: If matplotlib and latex are not installed, png-data won't be available. If a latex string is provided, qtconsole will then try to use matplotlib. It will not fall back to pretty printing after getting None. (I think this is a bug.)

So it seems that, if matplotlib and latex are not installed, we should provide notebook with a latex string but let qtconsole only have the (pretty) string. However, there is a problem. Quoting from this thread:

We do our best in IPython prevent the kernel from knowing to which kind of frontend is connected, and actually you can even have a kernel connected to differents frontend at the same time.

This leaves the question: which (common) default should be chosen for notebook and qtconsole when both matplotlib and latex are missing, use_latex='mathjax' or use_latex=False?

[moorepants]

notebook: Newer versions of notebook load MathJax from the net. It does not matter if neither matplotlib nor latex is available. It will suffice to provide IPython with a latex representation of the output.

I don't necessarily agree with this. I'd like it to "work" without an internet connection too.

qtconsole: If matplotlib and latex are not installed, png-data won't be available. If a latex string is provided, qtconsole will then try to use matplotlib. It will not fall back to pretty printing after getting None. (I think this is a bug.)

Agreed.

This leaves the question: which (common) default should be chosen for notebook and qtconsole when both matplotlib and latex are missing, use_latex='mathjax' or use_latex=False?

Maybe pretty print? But is it possible everything isn't installed for that to work too? Maybe it should just be the simple string rep.

[jksuom]

I'd like it to "work" without an internet connection too.

I was just referring to how the designers of notebook seem to have planned it. An alternative is a local installation of MathJax. But that is big, of course...

As to the default, I think text/plain should perhaps be taken even if MathJax could give nicer output in notebook. Anyway, a notebook user will always have the option of running init_printing(use_latex='mathjax').

[jksuom]

A possible plan for IPython notebook and qtconsole printing defaults (when use_latex=None).

• If both latex and dvipng are available, set use_latex=True to enable png-formatting in SymPy.
• Else if matplotlib is available, set use_latex='matplotlib' to enable png-formatting in IPython.
• Else set use_latex=False to fall back to text/plain-formatting in SymPy. (Always configured, pretty by default. Custom pretty_printer can be set.)

These defaults may always be overridden by setting use_latex. For example, notebook users can choose mathjax.

[asmeurer]

The upstream bug in the qtconsole has been fixed. See also the related jupyter/qtconsole#95.