matplotlib
diff --git a/‎lib/matplotlib/axes/_axes.py
Lines changed: 18 additions & 7 deletions b/‎lib/matplotlib/axes/_axes.py
Lines changed: 18 additions & 7 deletions
diff --git a/‎lib/matplotlib/tests/test_axes.py
Lines changed: 16 additions & 0 deletions b/‎lib/matplotlib/tests/test_axes.py
Lines changed: 16 additions & 0 deletions
@@ -830,10 +830,10 @@ def axhline(self, y=0, xmin=0, xmax=1, **kwargs):
 
             >>> axhline(y=.5, xmin=0.25, xmax=0.75)
         """
+        self._check_scalars([xmin, xmax], ['xmin', 'xmax'])
         if "transform" in kwargs:
-            raise ValueError(
-                "'transform' is not allowed as a kwarg;"
-                + "axhline generates its own transform.")
+            raise ValueError("'transform' is not allowed as a kwarg; "
+                             "axhline generates its own transform.")
         ymin, ymax = self.get_ybound()
 
         # We need to strip away the units for comparison with
@@ -899,11 +899,10 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
 
             >>> axvline(x=.5, ymin=0.25, ymax=0.75)
         """
-
+        self._check_scalars([ymin, ymax], ['ymin', 'ymax'])
         if "transform" in kwargs:
-            raise ValueError(
-                "'transform' is not allowed as a kwarg;"
-                + "axvline generates its own transform.")
+            raise ValueError("'transform' is not allowed as a kwarg; "
+                             "axvline generates its own transform.")
         xmin, xmax = self.get_xbound()
 
         # We need to strip away the units for comparison with
@@ -918,6 +917,16 @@ def axvline(self, x=0, ymin=0, ymax=1, **kwargs):
         self._request_autoscale_view(scalex=scalex, scaley=False)
         return l
 
+    @staticmethod
+    def _check_scalars(vals, names):
+        # Helper method to check that vals are all scalars
+        for val, name in zip(vals, names):
+            try:
+                float(val)
+            except Exception as e:
+                raise ValueError(f"{name} must be a single scalar value, "
+                                 f"but got {val}") from e
+
     @docstring.dedent_interpd
     def axline(self, xy1, xy2=None, *, slope=None, **kwargs):
         """
@@ -1038,6 +1047,7 @@ def axhspan(self, ymin, ymax, xmin=0, xmax=1, **kwargs):
         --------
         axvspan : Add a vertical span across the axes.
         """
+        self._check_scalars([xmin, xmax], ['xmin', 'xmax'])
         trans = self.get_yaxis_transform(which='grid')
 
         # process the unit information
@@ -1098,6 +1108,7 @@ def axvspan(self, xmin, xmax, ymin=0, ymax=1, **kwargs):
         >>> axvspan(1.25, 1.55, facecolor='g', alpha=0.5)
 
         """
+        self._check_scalars([ymin, ymax], ['ymin', 'ymax'])
         trans = self.get_xaxis_transform(which='grid')
 
         # process the unit information
 
@@ -4251,6 +4251,22 @@ def test_vline_limit():
     assert_allclose(ax.get_ylim(), (-.1, .2))
 
 
+@pytest.mark.parametrize('fv, fh, args', [[plt.axvline, plt.axhline, (1,)],
+                                          [plt.axvspan, plt.axhspan, (1, 1)]])
+def test_axline_minmax(fv, fh, args):
+    bad_lim = matplotlib.dates.num2date(1)
+    # Check vertical functions
+    with pytest.raises(ValueError, match='ymin must be a single scalar value'):
+        fv(*args, ymin=bad_lim, ymax=1)
+    with pytest.raises(ValueError, match='ymax must be a single scalar value'):
+        fv(*args, ymin=1, ymax=bad_lim)
+    # Check horizontal functions
+    with pytest.raises(ValueError, match='xmin must be a single scalar value'):
+        fh(*args, xmin=bad_lim, xmax=1)
+    with pytest.raises(ValueError, match='xmax must be a single scalar value'):
+        fh(*args, xmin=1, xmax=bad_lim)
+
+
 def test_empty_shared_subplots():
     # empty plots with shared axes inherit limits from populated plots
     fig, axs = plt.subplots(nrows=1, ncols=2, sharex=True, sharey=True)