Time series plot fails with non-standard calendars

[pgf]

It seems UltraPlot doesn't handle non-standard calendars when dealing with DataArray time series.
xarray makes use of cftime instead of numpy.datetime64 for non-standard calendars (see xarray docs, Time series data

import numpy            as np
import xarray           as xr
import ultraplot        as uplt

# Time axis centered at mid-month
# Standard calendar
time1=xr.date_range("2000-01", periods=120, freq="MS")
time2=xr.date_range("2000-02", periods=120, freq="MS")
time=time1+0.5*(time2-time1)
# Non-standard calendar (uses cftime)
time1=xr.date_range("2000-01", periods=120, freq="MS", calendar="noleap")
time2=xr.date_range("2000-02", periods=120, freq="MS", calendar="noleap")
time_noleap=time1+0.5*(time2-time1)

da=xr.DataArray(data=np.sin(np.arange(0.,2*np.pi,np.pi/60.)),
               dims=("time",),
               coords={"time":time,},
               attrs={"long_name":"low freq signal", "units":"normalized"})

da_noleap=xr.DataArray(data=np.sin(2.*np.arange(0.,2*np.pi,np.pi/60.)),
               dims=("time",),
               coords={"time":time_noleap,},
               attrs={"long_name":"high freq signal", "units":"normalized"})

fig,axs = uplt.subplots(ncols=2)
axs.format(title=("Standard calendar", "Non-standard calendar"))
axs[0].plot(da)
axs[1].plot(da_noleap)

Result:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[1], line 28
     26 axs.format(title=("Standard calendar", "Non-standard calendar"))
     27 axs[0].plot(da)
---> 28 axs[1].plot(da_noleap)

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/internals/inputs.py:365](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/internals/inputs.py#line=364), in _preprocess_or_redirect.<locals>._decorator.<locals>._preprocess_or_redirect(self, *args, **kwargs)
    363     kwargs["color"] = color
    364 # Call main function
--> 365 return func(self, *args, **kwargs)

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py:3673](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py#line=3672), in PlotAxes.plot(self, *args, **kwargs)
   3669 """
   3670 %(plot.plot)s
   3671 """
   3672 kwargs = _parse_vert(default_vert=True, **kwargs)
-> 3673 return self._apply_plot(*args, **kwargs)

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py:3390](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py#line=3389), in PlotAxes._apply_plot(self, vert, *pairs, **kwargs)
   3388 if fmt is not None:  # x1, y1, fmt1, x2, y2, fm2... style input
   3389     a.append(fmt)
-> 3390 (obj,) = self._call_native("plot", *a, **kw)
   3391 self._inbounds_xylim(extents, x, y)
   3392 objs.append((*eb, *es, obj) if eb or es else obj)

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py:1531](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/ultraplot/axes/plot.py#line=1530), in PlotAxes._call_native(self, name, *args, **kwargs)
   1529         obj = getattr(self.projection, name)(*args, ax=self, **kwargs)
   1530     else:
-> 1531         obj = getattr(super(), name)(*args, **kwargs)
   1532 return obj

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_axes.py:1779](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_axes.py#line=1778), in Axes.plot(self, scalex, scaley, data, *args, **kwargs)
   1777 lines = [*self._get_lines(self, *args, data=data, **kwargs)]
   1778 for line in lines:
-> 1779     self.add_line(line)
   1780 if scalex:
   1781     self._request_autoscale_view("x")

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_base.py:2407](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_base.py#line=2406), in _AxesBase.add_line(self, line)
   2404 if line.get_clip_path() is None:
   2405     line.set_clip_path(self.patch)
-> 2407 self._update_line_limits(line)
   2408 if not line.get_label():
   2409     line.set_label(f'_child{len(self._children)}')


File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_base.py:2430](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/axes/_base.py#line=2429), in _AxesBase._update_line_limits(self, line)
   2426 def _update_line_limits(self, line):
   2427     """
   2428     Figures out the data limit of the given line, updating `.Axes.dataLim`.
   2429     """
-> 2430     path = line.get_path()
   2431     if path.vertices.size == 0:
   2432         return

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/lines.py:1052](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/lines.py#line=1051), in Line2D.get_path(self)
   1050 """Return the `~matplotlib.path.Path` associated with this line."""
   1051 if self._invalidy or self._invalidx:
-> 1052     self.recache()
   1053 return self._path

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/lines.py:689](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/lines.py#line=688), in Line2D.recache(self, always)
    687 if always or self._invalidx:
    688     xconv = self.convert_xunits(self._xorig)
--> 689     x = _to_unmasked_float_array(xconv).ravel()
    690 else:
    691     x = self._x

File [~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/cbook.py:1355](http://localhost:8888/lab/tree/tmp/~/Library/local/miniforge3/envs/py3cf/lib/python3.13/site-packages/matplotlib/cbook.py#line=1354), in _to_unmasked_float_array(x)
   1353     return np.ma.asarray(x, float).filled(np.nan)
   1354 else:
-> 1355     return np.asarray(x, float)

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

Setup:

cftime                              1.6.4            py313h93df234_1          conda-forge
numpy                               2.3.0            py313h41a2e72_0          conda-forge
python                              3.13.1           h4f43103_102_cp313       conda-forge
matplotlib                          3.10.3           py313h39782a4_0          conda-forge
ultraplot                           1.57.1           pyhd8ed1ab_0             conda-forge
xarray                              2025.6.1         pyhd8ed1ab_1             conda-forge

[cvanelteren]

Thanks for the snippet and context. I can confirm the bug. I moddified locally the decorator _to_numpy_array in inputs.py and can now render this:

Not too sure how the formatting should look like for non-gregorian calendars, does this look ok?

[cvanelteren]

Actually without any edits you can run this

import numpy            as np
import xarray           as xr
import ultraplot        as uplt
import nc_time_axis 
# Time axis centered at mid-month
# Standard calendar
time1=xr.date_range("2000-01", periods=120, freq="MS")
time2=xr.date_range("2000-02", periods=120, freq="MS")
time=time1+0.5*(time2-time1)
# Non-standard calendar (uses cftime)
time1=xr.date_range("2000-01", periods=120, freq="MS", calendar="noleap")
time2=xr.date_range("2000-02", periods=120, freq="MS", calendar="noleap")
time_noleap=time1+0.5*(time2-time1)

da=xr.DataArray(data=np.sin(np.arange(0.,2*np.pi,np.pi/60.)),
               dims=("time",),
               coords={"time":time,},
               attrs={"long_name":"low freq signal", "units":"normalized"})

da_noleap=xr.DataArray(data=np.sin(2.*np.arange(0.,2*np.pi,np.pi/60.)),
               dims=("time",),
               coords={"time":time_noleap,},
               attrs={"long_name":"high freq signal", "units":"normalized"})

fig,axs = uplt.subplots(ncols=2)
axs.format(title=("Standard calendar", "Non-standard calendar"))
axs[0].plot(da)
axs[1].plot(da_noleap)

[cvanelteren]

or noleap

[cvanelteren]

The issue is that by default matplotlib does not support it and we would need to write a formatter registry for it which is provided by nc-time-axis. I opened a PR and we may need to bundle it to register the formatters.

[pgf]

Actually without any edits you can run this

import numpy as np
import xarray as xr
import ultraplot as uplt
import nc_time_axis

With the import of nc_time_axis it is closer to what it should look like.

[cvanelteren]

Closer is not completely, what are you missing? Perhaps I can assist.

[cvanelteren]

From the first range I see that we are formatting this on a year; the formatting for normal time ranges is handled by matplotlib which has support for the Gregorian calendar but not directly for non-Gregorian calendar. This means that we either have to move the formatting to UltraPlot but it would be easier to specify by the user; which would requiring specifying through nc-time-axis

[pgf]

Closer is not completely, what are you missing? Perhaps I can assist.

Sorry, I didn't elaborate much my answer.
I mean, the time coordinates (start, end, frequency, etc...) are identical except for the calendar. While I could live with the result above, I think the formatting of the x axis should be independent of the calendar, so the x axis on the right panel should be identical to the one on the left panel.

it would be easier to specify by the user; which would requiring specifying through nc-time-axis

I need to explore nc_time_axis. Can you provide an example?
Anyway, I think it would be more UltraPlotonic if this kind of details would be handled behind the scene.

[cvanelteren]

I agree. Need to explore their registers more to integrate it with ultraplot. I am generally in favor of adding it and would be relatively straight forward I hope.