Import nc_time_axis when needed

doc/whats-new.rst

@@ -35,6 +35,8 @@ Deprecations
 Bug fixes
 ~~~~~~~~~
 
+- Import ``nc_time_axis`` when needed (:issue:`7275`, :pull:`7276`).
+  By `Michael Niklas <https://github.com/headtr1ck>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/plot/utils.py

@@ -609,8 +609,8 @@ def _resolve_intervals_1dplot(
         remove_drawstyle = False
 
         # Convert intervals to double points
-        x_is_interval = _valid_other_type(xval, [pd.Interval])
-        y_is_interval = _valid_other_type(yval, [pd.Interval])
+        x_is_interval = _valid_other_type(xval, pd.Interval)
+        y_is_interval = _valid_other_type(yval, pd.Interval)
         if x_is_interval and y_is_interval:
             raise TypeError("Can't step plot intervals against intervals.")
         elif x_is_interval:
@@ -628,10 +628,10 @@ def _resolve_intervals_1dplot(
     else:
 
         # Convert intervals to mid points and adjust labels
-        if _valid_other_type(xval, [pd.Interval]):
+        if _valid_other_type(xval, pd.Interval):
             xval = _interval_to_mid_points(xval)
             x_suffix = "_center"
-        if _valid_other_type(yval, [pd.Interval]):
+        if _valid_other_type(yval, pd.Interval):
             yval = _interval_to_mid_points(yval)
             y_suffix = "_center"
 
@@ -646,7 +646,7 @@ def _resolve_intervals_2dplot(val, func_name):
     increases length by 1.
     """
     label_extra = ""
-    if _valid_other_type(val, [pd.Interval]):
+    if _valid_other_type(val, pd.Interval):
         if func_name == "pcolormesh":
             val = _interval_to_bound_points(val)
         else:
@@ -656,11 +656,13 @@ def _resolve_intervals_2dplot(val, func_name):
     return val, label_extra
 
 
-def _valid_other_type(x, types):
+def _valid_other_type(
+    x: ArrayLike, types: type[object] | tuple[type[object], ...]
+) -> bool:
     """
     Do all elements of x have a type from types?
     """
-    return all(any(isinstance(el, t) for t in types) for el in np.ravel(x))
+    return all(isinstance(el, types) for el in np.ravel(x))
 
 
 def _valid_numpy_subdtype(x, numpy_types):
@@ -675,47 +677,49 @@ def _valid_numpy_subdtype(x, numpy_types):
     return any(np.issubdtype(x.dtype, t) for t in numpy_types)
 
 
-def _ensure_plottable(*args):
+def _ensure_plottable(*args) -> None:
     """
     Raise exception if there is anything in args that can't be plotted on an
     axis by matplotlib.
     """
-    numpy_types = [
+    numpy_types: tuple[type[object], ...] = (
         np.floating,
         np.integer,
         np.timedelta64,
         np.datetime64,
         np.bool_,
         np.str_,
-    ]
-    other_types = [datetime]
-    if cftime is not None:
-        cftime_datetime_types = [cftime.datetime]
-        other_types = other_types + cftime_datetime_types
-    else:
-        cftime_datetime_types = []
+    )
+    other_types: tuple[type[object], ...] = (datetime,)
+    cftime_datetime_types: tuple[type[object], ...] = (
+        () if cftime is None else (cftime.datetime,)
+    )
+    other_types += cftime_datetime_types
+
     for x in args:
         if not (
-            _valid_numpy_subdtype(np.array(x), numpy_types)
-            or _valid_other_type(np.array(x), other_types)
+            _valid_numpy_subdtype(np.asarray(x), numpy_types)
+            or _valid_other_type(np.asarray(x), other_types)
         ):
             raise TypeError(
                 "Plotting requires coordinates to be numeric, boolean, "
                 "or dates of type numpy.datetime64, "
                 "datetime.datetime, cftime.datetime or "
-                f"pandas.Interval. Received data of type {np.array(x).dtype} instead."
-            )
-        if (
-            _valid_other_type(np.array(x), cftime_datetime_types)
-            and not nc_time_axis_available
-        ):
-            raise ImportError(
-                "Plotting of arrays of cftime.datetime "
-                "objects or arrays indexed by "
-                "cftime.datetime objects requires the "
-                "optional `nc-time-axis` (v1.2.0 or later) "
-                "package."
+                f"pandas.Interval. Received data of type {np.asarray(x).dtype} instead."
             )
+        if _valid_other_type(np.asarray(x), cftime_datetime_types):
+            if nc_time_axis_available:
+                # Register cftime datetypes to matplotlib.units.registry,
+                # otherwise matplotlib will raise an error:
+                import nc_time_axis  # noqa: F401
+            else:
+                raise ImportError(
+                    "Plotting of arrays of cftime.datetime "
+                    "objects or arrays indexed by "
+                    "cftime.datetime objects requires the "
+                    "optional `nc-time-axis` (v1.2.0 or later) "
+                    "package."
+                )
 
 
 def _is_numeric(arr):

xarray/tests/__init__.py

@@ -68,7 +68,6 @@ def _importorskip(
 has_cftime, requires_cftime = _importorskip("cftime")
 has_dask, requires_dask = _importorskip("dask")
 has_bottleneck, requires_bottleneck = _importorskip("bottleneck")
-has_nc_time_axis, requires_nc_time_axis = _importorskip("nc_time_axis")
 has_rasterio, requires_rasterio = _importorskip("rasterio")
 has_zarr, requires_zarr = _importorskip("zarr")
 has_fsspec, requires_fsspec = _importorskip("fsspec")

xarray/tests/test_plot.py

@@ -14,6 +14,7 @@
 import xarray as xr
 import xarray.plot as xplt
 from xarray import DataArray, Dataset
+from xarray.core.utils import module_available
 from xarray.plot.dataarray_plot import _infer_interval_breaks
 from xarray.plot.dataset_plot import _infer_meta_data
 from xarray.plot.utils import (
@@ -29,14 +30,15 @@
 from . import (
     assert_array_equal,
     assert_equal,
-    has_nc_time_axis,
     requires_cartopy,
     requires_cftime,
     requires_matplotlib,
-    requires_nc_time_axis,
     requires_seaborn,
 )
 
+# this should not be imported to test if the automatic lazy import works
+has_nc_time_axis = module_available("nc_time_axis")
+
 # import mpl and change the backend before other mpl imports
 try:
     import matplotlib as mpl
@@ -2823,8 +2825,8 @@ def test_datetime_plot2d(self) -> None:
 
 
 @pytest.mark.filterwarnings("ignore:setting an array element with a sequence")
-@requires_nc_time_axis
 @requires_cftime
+@pytest.mark.skipif(not has_nc_time_axis, reason="nc_time_axis is not installed")
 class TestCFDatetimePlot(PlotTestCase):
     @pytest.fixture(autouse=True)
     def setUp(self) -> None:
@@ -3206,7 +3208,7 @@ def test_plot_empty_raises(val: list | float, method: str) -> None:
 
 
 @requires_matplotlib
-def test_facetgrid_axes_raises_deprecation_warning():
+def test_facetgrid_axes_raises_deprecation_warning() -> None:
     with pytest.warns(
         DeprecationWarning,
         match=(

xarray/tests/test_plugins.py

@@ -203,6 +203,7 @@ def test_lazy_import() -> None:
         "scipy",
         "zarr",
         "matplotlib",
+        "nc_time_axis",
         "flox",
         # "dask",  # TODO: backends.locks is not lazy yet :(
         "dask.array",