matplotlib
diff --git a/‎doc/api/next_api_changes/deprecations.rst
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diff --git a/‎lib/matplotlib/axes/_axes.py
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diff --git a/‎lib/matplotlib/collections.py
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+24-16Lines changed: 24 additions & 16 deletions b/‎lib/matplotlib/collections.py
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diff --git a/‎lib/matplotlib/tests/test_axes.py
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@@ -415,3 +415,10 @@ parent figure, though they can be later removed with ``ax.remove()``.
 
 ``.BboxBase.inverse_transformed`` is deprecated (call `.BboxBase.transformed`
 on the `~.Transform.inverted()` transform instead).
+
+*orientation* of ``eventplot()`` and `.EventCollection`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Setting the *orientation* of an ``eventplot()`` or `.EventCollection` to "none"
+or None is deprecated; set it to "horizontal" instead.  Moreover, the two
+orientations ("horizontal" and "vertical") will become case-sensitive in the
+future.
@@ -1264,7 +1264,7 @@ def eventplot(self, positions, orientation='horizontal', lineoffsets=1,
             row corresponds to a row or a column of lines (depending on the
             *orientation* parameter).
 
-        orientation : {'horizontal', 'vertical'}, optional
+        orientation : {'horizontal', 'vertical'}, default: 'horizontal'
             The direction of the event collections:
 
             - 'horizontal': the lines are arranged horizontally in rows,
 
@@ -1455,8 +1455,8 @@ class EventCollection(LineCollection):
     _edge_default = True
 
     def __init__(self,
-                 positions,     # Cannot be None.
-                 orientation=None,
+                 positions,  # Cannot be None.
+                 orientation='horizontal',
                  lineoffset=0,
                  linelength=1,
                  linewidth=None,
@@ -1471,10 +1471,9 @@ def __init__(self,
         positions : 1D array-like
             Each value is an event.
 
-        orientation : {None, 'horizontal', 'vertical'}, optional
+        orientation : {'horizontal', 'vertical'}, default: 'horizontal'
             The orientation of the **collection** (the event bars are along
-            the orthogonal direction). Defaults to 'horizontal' if not
-            specified or None.
+            the orthogonal direction).
 
         lineoffset : scalar, default: 0
             The offset of the center of the markers from the origin, in the
@@ -1584,17 +1583,26 @@ def set_orientation(self, orientation=None):
 
         Parameters
         ----------
-        orientation: {'horizontal', 'vertical'} or None
-            Defaults to 'horizontal' if not specified or None.
-        """
-        if (orientation is None or orientation.lower() == 'none' or
-                orientation.lower() == 'horizontal'):
-            is_horizontal = True
-        elif orientation.lower() == 'vertical':
-            is_horizontal = False
-        else:
-            cbook._check_in_list(['horizontal', 'vertical'],
-                                 orientation=orientation)
+        orientation : {'horizontal', 'vertical'}
+        """
+        try:
+            is_horizontal = cbook._check_getitem(
+                {"horizontal": True, "vertical": False},
+                orientation=orientation)
+        except ValueError:
+            if (orientation is None or orientation.lower() == "none"
+                    or orientation.lower() == "horizontal"):
+                is_horizontal = True
+            elif orientation.lower() == "vertical":
+                is_horizontal = False
+            else:
+                raise
+            normalized = "horizontal" if is_horizontal else "vertical"
+            cbook.warn_deprecated(
+                "3.3", message="Support for setting the orientation of "
+                f"EventCollection to {orientation!r} is deprecated since "
+                f"%(since)s and will be removed %(removal)s; please set it to "
+                f"{normalized!r} instead.")
         if is_horizontal == self.is_horizontal():
             return
         self.switch_orientation()
 
@@ -3848,14 +3848,16 @@ def test_empty_eventplot():
     plt.draw()
 
 
-@pytest.mark.parametrize('data, orientation', product(
-    ([[]], [[], [0, 1]], [[0, 1], []]),
-    ('_empty', 'vertical', 'horizontal', None, 'none')))
+@pytest.mark.parametrize('data', [[[]], [[], [0, 1]], [[0, 1], []]])
+@pytest.mark.parametrize(
+    'orientation', ['_empty', 'vertical', 'horizontal', None, 'none'])
 def test_eventplot_orientation(data, orientation):
     """Introduced when fixing issue #6412."""
     opts = {} if orientation == "_empty" else {'orientation': orientation}
     fig, ax = plt.subplots(1, 1)
-    ax.eventplot(data, **opts)
+    with (pytest.warns(MatplotlibDeprecationWarning)
+          if orientation in [None, 'none'] else nullcontext()):
+        ax.eventplot(data, **opts)
     plt.draw()