[fix] Spine.set_bounds() does not take parameter **None** as expected (matplotlib#30330)

* extract a _get_bounds_or_viewLim function, which is used both in set_bounds and _adjust_location

* add tests

* add doc str for _get_bounds_or_viewLim

* Update lib/matplotlib/tests/test_spines.py

Set appropriate bottom_bound in the test.

Co-authored-by: Ruth Comer <10599679+rcomer@users.noreply.github.com>

* Update lib/matplotlib/spines.py

The error is mainly raised for user- or third party-defined spines. 'circle' is already handled in two function callers.

Co-authored-by: Ruth Comer <10599679+rcomer@users.noreply.github.com>

* regroup spine tests

---------

Co-authored-by: Ruth Comer <10599679+rcomer@users.noreply.github.com>

Author: leakyH

lib/matplotlib/spines.py

@@ -232,20 +232,30 @@ def _clear(self):
         """
         self._position = None  # clear position
 
-    def _adjust_location(self):
-        """Automatically set spine bounds to the view interval."""
-
-        if self.spine_type == 'circle':
-            return
+    def _get_bounds_or_viewLim(self):
+        """
+        Get the bounds of the spine.
 
+        If self._bounds is None, return self.axes.viewLim.intervalx
+        or self.axes.viewLim.intervaly based on self.spine_type
+        """
         if self._bounds is not None:
             low, high = self._bounds
         elif self.spine_type in ('left', 'right'):
             low, high = self.axes.viewLim.intervaly
         elif self.spine_type in ('top', 'bottom'):
             low, high = self.axes.viewLim.intervalx
         else:
-            raise ValueError(f'unknown spine spine_type: {self.spine_type}')
+            raise ValueError(f'spine_type: {self.spine_type} not supported')
+        return low, high
+
+    def _adjust_location(self):
+        """Automatically set spine bounds to the view interval."""
+
+        if self.spine_type == 'circle':
+            return
+
+        low, high = self._get_bounds_or_viewLim()
 
         if self._patch_type == 'arc':
             if self.spine_type in ('bottom', 'top'):
@@ -424,7 +434,7 @@ def set_bounds(self, low=None, high=None):
                 'set_bounds() method incompatible with circular spines')
         if high is None and np.iterable(low):
             low, high = low
-        old_low, old_high = self.get_bounds() or (None, None)
+        old_low, old_high = self._get_bounds_or_viewLim()
         if low is None:
             low = old_low
         if high is None:

lib/matplotlib/tests/test_spines.py

@@ -166,3 +166,32 @@ def test_arc_spine_inner_no_axis():
     assert ax.spines["inner"].axis is None
 
     fig.draw_without_rendering()
+
+
+def test_spine_set_bounds_with_none():
+    """Test that set_bounds(None, ...) uses original axis view limits."""
+    fig, ax = plt.subplots()
+
+    # Plot some data to set axis limits
+    x = np.linspace(0, 10, 100)
+    y = np.sin(x)
+    ax.plot(x, y)
+
+    xlim = ax.viewLim.intervalx
+    ylim = ax.viewLim.intervaly
+    # Use modified set_bounds with None
+    ax.spines['bottom'].set_bounds(2, None)
+    ax.spines['left'].set_bounds(None, None)
+
+    # Check that get_bounds returns correct numeric values
+    bottom_bound = ax.spines['bottom'].get_bounds()
+    assert bottom_bound[1] is not None, "Higher bound should be numeric"
+    assert np.isclose(bottom_bound[0], 2), "Lower bound should match provided value"
+    assert np.isclose(bottom_bound[1],
+                       xlim[1]), "Upper bound should match original value"
+
+    left_bound = ax.spines['left'].get_bounds()
+    assert (left_bound[0] is not None) and (left_bound[1] is not None), \
+        "left bound should be numeric"
+    assert np.isclose(left_bound[0], ylim[0]), "Lower bound should match original value"
+    assert np.isclose(left_bound[1], ylim[1]), "Upper bound should match original value"