REG: nc_time_axis not imported anymore

[aulemahal]

What happened?

With xarray 2022.11.0, plotting a DataArray with a cftime time axis fails.

It fails with a matplotlib error : TypeError: float() argument must be a string or a real number, not 'cftime._cftime.DatetimeNoLeap'

What did you expect to happen?

With previous versions of xarray, the nc_time_axis package was imported by xarray and these errors were avoided.

Minimal Complete Verifiable Example

import xarray as xr
da = xr.DataArray(
    list(range(10)),
    dims=('time',),
    coords={'time': xr.cftime_range('1900-01-01', periods=10, calendar='noleap', freq='D')}
)
da.plot()

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In [1], line 7
      1 import xarray as xr
      2 da = xr.DataArray(
      3     list(range(10)),
      4     dims=('time',),
      5     coords={'time': xr.cftime_range('1900-01-01', periods=10, calendar='noleap', freq='D')}
      6 )
----> 7 da.plot()

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/xarray/plot/accessor.py:46, in DataArrayPlotAccessor.__call__(self, **kwargs)
     44 @functools.wraps(dataarray_plot.plot, assigned=("__doc__", "__annotations__"))
     45 def __call__(self, **kwargs) -> Any:
---> 46     return dataarray_plot.plot(self._da, **kwargs)

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/xarray/plot/dataarray_plot.py:312, in plot(darray, row, col, col_wrap, ax, hue, subplot_kws, **kwargs)
    308     plotfunc = hist
    310 kwargs["ax"] = ax
--> 312 return plotfunc(darray, **kwargs)

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/xarray/plot/dataarray_plot.py:517, in line(darray, row, col, figsize, aspect, size, ax, hue, x, y, xincrease, yincrease, xscale, yscale, xticks, yticks, xlim, ylim, add_legend, _labels, *args, **kwargs)
    513 ylabel = label_from_attrs(yplt, extra=y_suffix)
    515 _ensure_plottable(xplt_val, yplt_val)
--> 517 primitive = ax.plot(xplt_val, yplt_val, *args, **kwargs)
    519 if _labels:
    520     if xlabel is not None:

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/axes/_axes.py:1664, in Axes.plot(self, scalex, scaley, data, *args, **kwargs)
   1662 lines = [*self._get_lines(*args, data=data, **kwargs)]
   1663 for line in lines:
-> 1664     self.add_line(line)
   1665 if scalex:
   1666     self._request_autoscale_view("x")

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/axes/_base.py:2340, in _AxesBase.add_line(self, line)
   2337 if line.get_clip_path() is None:
   2338     line.set_clip_path(self.patch)
-> 2340 self._update_line_limits(line)
   2341 if not line.get_label():
   2342     line.set_label(f'_child{len(self._children)}')

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/axes/_base.py:2363, in _AxesBase._update_line_limits(self, line)
   2359 def _update_line_limits(self, line):
   2360     """
   2361     Figures out the data limit of the given line, updating self.dataLim.
   2362     """
-> 2363     path = line.get_path()
   2364     if path.vertices.size == 0:
   2365         return

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/lines.py:1031, in Line2D.get_path(self)
   1029 """Return the `~matplotlib.path.Path` associated with this line."""
   1030 if self._invalidy or self._invalidx:
-> 1031     self.recache()
   1032 return self._path

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/lines.py:659, in Line2D.recache(self, always)
    657 if always or self._invalidx:
    658     xconv = self.convert_xunits(self._xorig)
--> 659     x = _to_unmasked_float_array(xconv).ravel()
    660 else:
    661     x = self._x

File ~/mambaforge/envs/xclim/lib/python3.10/site-packages/matplotlib/cbook/__init__.py:1369, in _to_unmasked_float_array(x)
   1367     return np.ma.asarray(x, float).filled(np.nan)
   1368 else:
-> 1369     return np.asarray(x, float)

TypeError: float() argument must be a string or a real number, not 'cftime._cftime.DatetimeNoLeap'

Anything else we need to know?

I suspect #7179.

This line:

xarray/xarray/plot/utils.py

Line 27 in cc7e09a

nc_time_axis_available = module_available("nc_time_axis")

does not import nc_time_axis. Further down, the variable gets checked and if False an error is raised, but if the package still is not imported if True.

Previously we had:

xarray/xarray/plot/utils.py

Lines 27 to 32 in fc9026b

	try:
	import nc_time_axis # noqa: F401
	nc_time_axis_available = True
	except ImportError:
	nc_time_axis_available = False

where the package is always imported.

Maybe there's a way to import nc_time_axis only when needed?

Environment

INSTALLED VERSIONS

commit: None
python: 3.10.6 | packaged by conda-forge | (main, Aug 22 2022, 20:36:39) [GCC 10.4.0]
python-bits: 64
OS: Linux
OS-release: 6.0.5-200.fc36.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: fr_CA.UTF-8
LOCALE: ('fr_CA', 'UTF-8')
libhdf5: 1.12.2
libnetcdf: 4.8.1

xarray: 2022.11.0
pandas: 1.5.1
numpy: 1.23.4
scipy: 1.8.1
netCDF4: 1.6.1
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: 1.6.2
nc_time_axis: 1.4.1
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: 1.3.5
dask: 2022.10.2
distributed: 2022.10.2
matplotlib: 3.6.2
cartopy: None
seaborn: None
numbagg: None
fsspec: 2022.10.0
cupy: None
pint: 0.20.1
sparse: None
flox: None
numpy_groupies: None
setuptools: 65.5.1
pip: 22.3.1
conda: None
pytest: 7.2.0
IPython: 8.6.0
sphinx: 5.3.0

[headtr1ck]

Thanks for the find :)
That indeed is a bug.
Always difficult to keep track of such packages that are not actively used but need to be imported to register things in matplotlib.

I took the freedom to use your example as a new test.