Fix Latex support

[ccordoba12]

Fixes #56

This builds on top of ipython/ipython#9203, so that one has to be merged first.

Pinging @flying-sheep, @asmeurer and @jorisvandenbossche

---

Tasks:

• Fix the case when neither Matplotlib nor Latex are installed. Qtconsole was displaying an empty image when it should move to use the plain text repr.
• Fix the case when Matplotlib is incapable of handling Latex. Qtconsole was printing a huge traceback, even after pull request Fallback to the string printer if the latex printer raises an exception #65 .
• Fix the case when Latex doesn't come in math mode. This will fix the issues with IRKernel and Pandas.
• Bonus: First try to use Latex, then Matplotlib to generate the representation.

[minrk]

Isn't it a good thing to log failure to render the latex?

[flying-sheep]

yeah, i think we should keep catching all exceptions and only in case of a ValueError (or probably a custom subclass we define) we swallow the error (as this one means that we got non-equation LaTeX)

[ccordoba12]

Isn't it a good thing to log failure to render the latex?

Not for Spyder and Canopy because those failures are shown in the terminal where those applications were started. If they are started graphically, the errors won't be seen by their users.

Besides, (as I said in ipython/ipython#9203) possible errors are:

1. Matplotlib is unable to handle Latex, something not easily discernible from the traceback.
2. Latex has syntax errors, something that also generates one of those long and almost unreadable report errors.

So this simplifies things and handles all cases I mentioned at the beginning correctly.

[ccordoba12]

or probably a custom subclass we define

Yes, I was thinking to create a simple LatexError class.

[flying-sheep]

good points. it’s the latex-repr-writers’ responsibility to emit correct code anyway and if they don’t, they’ll have to debug it.

[asmeurer]

Regarding the last checkmark, it's worth noting that matplotlib's math renderer produces output that's considerably worse than latex. Example:

matplotlib

latex

For SymPy we prefer latex and only fallback to matplotlib if it isn't installed.

[minrk]

@asmeurer thanks, following sympy's lead seems sensible here.

[ccordoba12]

Thanks @asmeurer for the input. I changed the task accordingly.

[flying-sheep]

OK, then the only thing left is the other mathmode triggers (which only work for the dvipng backend)

inline:

• \(...\)
• $...$
• environments (\begin{name}...\end{name}):
  • math

display:

• \[...\]
• $$...$$
• environments (\begin{name}...\end{name}):
  • displaymath
  • equation/equation*
  • eqnarray/eqnarray*
  • multline/multline*
  • gather/gather*
  • align/align*
  • flalign/flalign*
  • alignat/alignat*

[ccordoba12]

@flying-sheep, I won't implement all that, for two reasons:

1. Checking for dollar signs is enough for now, i.e. to have Sympy, IRKernel and Pandas work as expected.
2. I don't have time for it.

Maybe you could do it after this PR is merged :-)

[ccordoba12]

Or you could send a PR against my branch if you want it as part of this.

[flying-sheep]

no separately is OK

or let me do it inline

[ccordoba12]

Against my branch? Please be my guest :-)

In any case, thanks for helping me out.

[flying-sheep]

OK. here it is. is this sufficient or should i do the PR?

basic_envs = 'math displaymath'.split()
starable_envs = 'equation eqnarray multline gather align flalign alignat'.split()
star_envs = [env + '*' for env in starable_envs]
envs = basic_envs + starable_envs + star_envs

env_syntax = [r'\begin{{{0}}} \end{{{0}}}'.format(env).split() for env in envs]

math_syntax = [
    (r'\[', r'\]'), (r'\(', r'\)'),
    ('$$', '$$'), ('$', '$'),
]

def is_latex_math(latex):
    for start, end in math_syntax + env_syntax:
        inner = latex[len(start):-len(end)]
        if start in inner or end in inner:
            return False
        if latex.startswith(start) and latex.endswith(end):
            return True
    return False

[ccordoba12]

I think it's enough, thanks a lot!

[flying-sheep]

NP!

i edited it a bit since first commenting, so the version at the time of writing should be good

[ccordoba12]

@minrk, I think this one is ready. Please review it and let me know what you think.

[flying-sheep]

great, thanks!