issues: 1442443970

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

Python 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

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

Relevant log output

```Python

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: https://github.com/pydata/xarray/blob/cc7e09a3507fa342b3790b5c109e700fa12f0b17/xarray/plot/utils.py#L27 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: https://github.com/pydata/xarray/blob/fc9026b59d38146a21769cc2d3026a12d58af059/xarray/plot/utils.py#L27-L32 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