Use drawstyle instead of linestyle in plot.step.

Mixing the two is deprecated in Matplotlib 3.1, and breaks the doc build
if warnings are set to errors (which they are in new IPython sphinx
extensions.)

doc/whats-new.rst

@@ -20,7 +20,12 @@ v0.16.0 (unreleased)
 
 Breaking changes
 ~~~~~~~~~~~~~~~~
-
+- Alternate draw styles for :py:meth:`plot.step` must be passed using the
+  ``drawstyle`` (or ``ds``) keyword argument, instead of the ``linestyle`` (or
+  ``ls``) keyword argument, in line with the `upstream change in Matplotlib
+  <https://matplotlib.org/api/prev_api_changes/api_changes_3.1.0.html#passing-a-line2d-s-drawstyle-together-with-the-linestyle-is-deprecated>`_.
+  (:pull:`3274`)
+  By `Elliott Sales de Andrade <https://github.com/QuLogic>`_
 
 New Features
 ~~~~~~~~~~~~

xarray/plot/plot.py

@@ -329,7 +329,7 @@ def line(
     return primitive
 
 
-def step(darray, *args, where="pre", linestyle=None, ls=None, **kwargs):
+def step(darray, *args, where="pre", drawstyle=None, ds=None, **kwargs):
     """
     Step plot of DataArray index against values
 
@@ -359,16 +359,16 @@ def step(darray, *args, where="pre", linestyle=None, ls=None, **kwargs):
     if where not in {"pre", "post", "mid"}:
         raise ValueError("'where' argument to step must be " "'pre', 'post' or 'mid'")
 
-    if ls is not None:
-        if linestyle is None:
-            linestyle = ls
+    if ds is not None:
+        if drawstyle is None:
+            drawstyle = ds
         else:
-            raise TypeError("ls and linestyle are mutually exclusive")
-    if linestyle is None:
-        linestyle = ""
-    linestyle = "steps-" + where + linestyle
+            raise TypeError("ds and drawstyle are mutually exclusive")
+    if drawstyle is None:
+        drawstyle = ""
+    drawstyle = "steps-" + where + drawstyle
 
-    return line(darray, *args, linestyle=linestyle, **kwargs)
+    return line(darray, *args, drawstyle=drawstyle, **kwargs)
 
 
 def hist(

xarray/plot/utils.py

@@ -465,7 +465,7 @@ def _resolve_intervals_1dplot(xval, yval, xlabel, ylabel, kwargs):
     """
 
     # Is it a step plot? (see matplotlib.Axes.step)
-    if kwargs.get("linestyle", "").startswith("steps-"):
+    if kwargs.get("drawstyle", "").startswith("steps-"):
 
         # Convert intervals to double points
         if _valid_other_type(np.array([xval, yval]), [pd.Interval]):
@@ -476,7 +476,7 @@ def _resolve_intervals_1dplot(xval, yval, xlabel, ylabel, kwargs):
             yval, xval = _interval_to_double_bound_points(yval, xval)
 
         # Remove steps-* to be sure that matplotlib is not confused
-        del kwargs["linestyle"]
+        del kwargs["drawstyle"]
 
     # Is it another kind of plot?
     else:

xarray/tests/test_plot.py

@@ -591,6 +591,10 @@ def setUp(self):
     def test_step(self):
         self.darray[0, 0].plot.step()
 
+    @pytest.mark.parametrize("ds", ["pre", "post", "mid"])
+    def test_step_with_drawstyle(self, ds):
+        self.darray[0, 0].plot.step(drawstyle=ds)
+
     def test_coord_with_interval_step(self):
         """Test step plot with intervals."""
         bins = [-1, 0, 1, 2]