Support empty stairs.

anntzer · anntzer · commit 348d672d3fb7 · 2021-02-02T15:19:12.000+01:00
diff --git a/lib/matplotlib/patches.py b/lib/matplotlib/patches.py
@@ -988,7 +988,8 @@ def _update_path(self):
                              "Expected `len(values) + 1 == len(edges)`, but "
                              f"`len(values) = {self._values.size}` and "
                              f"`len(edges) = {self._edges.size}`.")
-        verts, codes = [], []
+        # Initializing with empty arrays allows supporting empty stairs.
+        verts, codes = [np.empty((0, 2))], [np.empty(0, dtype=Path.code_type)]
 
         _nan_mask = np.isnan(self._values)
         if self._baseline is not None:
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -1932,6 +1932,13 @@ def test_stairs_baseline_0(fig_test, fig_ref):
     ref_ax.set_ylim(0, None)
 
 
+def test_stairs_empty():
+    ax = plt.figure().add_subplot()
+    ax.stairs([], [42])
+    assert ax.get_xlim() == (39, 45)
+    assert ax.get_ylim() == (-0.06, 0.06)
+
+
 def test_stairs_invalid_nan():
     with pytest.raises(ValueError, match='Nan values in "edges"'):
         plt.stairs([1, 2], [0, np.nan, 1])
