Complex LaTeX expressions in `long_name`s aren't rendered correctly when plotting

[tomchor]

What happened:

When I try to give a variable a long_name that's a complex latex expression and then plot that variable the expression doesn't get rendered by latex

What you expected to happen:

I expected the name to get rendered by latex

Minimal Complete Verifiable Example:

In the example below I'm plotting a variable with a complex long_name via xarray and then plotting it again (in a separate figure) using only matplotlib and manually setting xlabel(). The matplotlib-only version works fine (right), but the xarray version doesn't render (left).

import numpy as np
from matplotlib import pyplot as plt
import xarray as xr
da = xr.DataArray(range(5), dims="x", coords = dict(x=range(5)))
name = r"$Ra_s = \mathrm{mean}(\epsilon_k) / \mu M^2_\infty$"
da.x.attrs = dict(long_name = name)
da.plot()

plt.figure()
plt.plot(range(5))
plt.xlabel(name)

Anything else we need to know?:

Environment:

Output of xr.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.9.2 (default, Mar 3 2021, 20:02:32)
[GCC 7.3.0]
python-bits: 64
OS: Linux
OS-release: 5.10.53-1-MANJARO
machine: x86_64
processor:
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8
libhdf5: 1.10.6
libnetcdf: 4.6.1

xarray: 0.17.0
pandas: 1.2.3
numpy: 1.19.2
scipy: 1.5.3
netCDF4: 1.5.6
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.2.1
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.2
dask: 2021.04.0
distributed: 2021.04.0
matplotlib: 3.3.4
cartopy: 0.18.0
seaborn: None
numbagg: None
pint: 0.17
setuptools: 52.0.0.post20210125
pip: 21.0.1
conda: None
pytest: None
IPython: 7.22.0
sphinx: None

[tomchor]

Note that for simple latex expressions xarray appears to work fine. For example name = r"$\mathrm{mean}(\epsilon_k)$" works in both figures in the example above.

[dcherian]

I agree this is annoying but there is no good solution AFAIK.

We use textwrap here:

xarray/xarray/plot/utils.py

Line 493 in 8b95da8

return "\n".join(textwrap.wrap(name + extra + units, 30))

I guess we could skip it if the first character in name is $?

[tomchor]

I'm not entirely sure why that would make the LaTeX renderer fail. But if that's the case and skipping it is an option, I'd test that both the first and last characters are $ before skipping.

[Illviljan]

It's the newline join that's the problem. You can get the latex working as textwrap intends by using "$\n$".join

import numpy as np
from matplotlib import pyplot as plt
import xarray as xr
da = xr.DataArray(range(5), dims="x", coords = dict(x=range(5)))
name = r"$Ra_s = \mathrm{mean}(\epsilon_k) / \mu M^2_\infty$"
name = "$\n$".join(textwrap.wrap(name, 30))
da.x.attrs = dict(long_name = name)
da.plot()

plt.figure()
plt.plot(range(5))
plt.xlabel(name)

But that looks worse than the original, checking if the string is latex-able seems a good idea.

[keewis]

should have been closed by #5682