FIX: colorbar pad for ImageGrid

Author: mathause

doc/users/next_whats_new/mpl_toolkit_colorbar_pad.rst

@@ -0,0 +1,6 @@
+Fix padding of single colorbar for ``ImageGrid``
+------------------------------------------------
+
+``ImageGrid`` with ``cbar_mode="single"`` no longer adds the ``axes_pad`` between the
+axes and the colorbar for thr ``cbar_location`` left and bottom. Add required space
+using `cbar_pad` instead.

lib/mpl_toolkits/axes_grid1/axes_grid.py

@@ -358,6 +358,11 @@ def __init__(self, fig,
         cbar_location : {"left", "right", "bottom", "top"}, default: "right"
         cbar_pad : float, default: None
             Padding between the image axes and the colorbar axes.
+
+            .. versionchanged:: 3.10
+                `cbar_mode="single"` no longer adds the `axes_pad` between the axes and
+                the colorbar if the `cbar_location` is `"left"` or `"bottom"`
+
         cbar_size : size specification (see `.Size.from_any`), default: "5%"
             Colorbar size.
         cbar_set_cax : bool, default: True
@@ -439,7 +444,7 @@ def _init_locators(self):
             self.cbar_axes[0].set_visible(True)
 
         for col, ax in enumerate(self.axes_row[0]):
-            if h:
+            if col != 0:
                 h.append(self._horiz_pad_size)
 
             if ax:
@@ -468,7 +473,7 @@ def _init_locators(self):
         v_ax_pos = []
         v_cb_pos = []
         for row, ax in enumerate(self.axes_column[0][::-1]):
-            if v:
+            if row != 0:
                 v.append(self._vert_pad_size)
 
             if ax:

lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py

@@ -424,7 +424,7 @@ def test_image_grid_single_bottom():
 
     fig = plt.figure(1, (2.5, 1.5))
     grid = ImageGrid(fig, (0, 0, 1, 1), nrows_ncols=(1, 3),
-                     axes_pad=(0.2, 0.15), cbar_mode="single",
+                     axes_pad=(0.2, 0.15), cbar_mode="single", cbar_pad=0.3,
                      cbar_location="bottom", cbar_size="10%", label_mode="1")
     # 4-tuple rect => Divider, isinstance will give True for SubplotDivider
     assert type(grid.get_divider()) is Divider