Make all parameters of ColorbarBase, except ax, keyword-only.

anntzer · anntzer · commit 6a70bebce3ed · 2020-04-18T20:41:26.000+02:00
This is consistent with Colorbar.  Moreover, this will make it possibly
to ultimately merge Colorbar into ColorbarBase -- currently, they only
differ by the fact that a ColorbarBase doesn't have an associated
ScalarMappable, but we can just construct an empty ScalarMappable in
that case (this is already what we document as recommended approach to
construct colorbars not attached to an artist --
`fig.colorbar(ScalarMappable(norm=..., cmap=...))`.  Right now this
merging is *nearly* possible except for the fact that the constructors'
signatures are a pain to combine.
diff --git a/doc/api/api_changes_3.3/deprecations.rst b/doc/api/api_changes_3.3/deprecations.rst
@@ -455,3 +455,8 @@ replaced by calls to ``draw_idle()`` on the corresponding canvas.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
 The ``add_checker`` and ``check_update`` methods and ``update_dict`` attribute
 of `.ScalarMappable` are deprecated.
+
+``ColorbarBase`` parameters will become keyword-only
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+All parameters of ``ColorbarBase``, except for the first (*ax*), will become
+keyword-only, consistently with ``Colorbar``.
diff --git a/lib/matplotlib/colorbar.py b/lib/matplotlib/colorbar.py
@@ -394,6 +394,7 @@ class ColorbarBase:
 
     n_rasterize = 50  # rasterize solids if number of colors >= n_rasterize
 
+    @cbook._make_keyword_only("3.3", "cmap")
     def __init__(self, ax, cmap=None,
                  norm=None,
                  alpha=None,
diff --git a/lib/matplotlib/tests/test_colorbar.py b/lib/matplotlib/tests/test_colorbar.py
@@ -226,7 +226,7 @@ def test_remove_from_figure(use_gridspec):
 def test_colorbarbase():
     # smoke test from #3805
     ax = plt.gca()
-    ColorbarBase(ax, plt.cm.bone)
+    ColorbarBase(ax, cmap=plt.cm.bone)
 
 
 @image_comparison(['colorbar_closed_patch'], remove_text=True)
