Fix for inverted bokeh colormaps and matplotlib Colormap instances

holoviews/plotting/mpl/element.py

@@ -657,13 +657,14 @@ def _norm_kwargs(self, element, ranges, opts, vdim, prefix=''):
                     color = color[:-2]
                 colors[k] = {'color': color, 'alpha': alpha}
 
-        if isinstance(cmap, dict):
-            factors = np.unique(values)
-            palette = [cmap.get(f, colors.get('NaN', {'color': self._default_nan})['color'])
-                       for f in factors]
-        else:
-            palette = process_cmap(cmap, self.color_levels)
-        cmap = mpl_colors.ListedColormap(palette)
+        if not isinstance(cmap, mpl_colors.Colormap):
+            if isinstance(cmap, dict):
+                factors = np.unique(values)
+                palette = [cmap.get(f, colors.get('NaN', {'color': self._default_nan})['color'])
+                           for f in factors]
+            else:
+                palette = process_cmap(cmap, self.color_levels)
+            cmap = mpl_colors.ListedColormap(palette)
         if 'max' in colors: cmap.set_over(**colors['max'])
         if 'min' in colors: cmap.set_under(**colors['min'])
         if 'NaN' in colors: cmap.set_bad(**colors['NaN'])

holoviews/plotting/util.py

@@ -495,7 +495,11 @@ def bokeh_palette_to_palette(cmap, ncolors=None):
     from bokeh import palettes
 
     # Handle categorical colormaps to avoid interpolation
-    categorical = ('category', 'dark', 'colorblind', 'pastel', 'set1', 'set2', 'set3', 'paired')
+    categorical = ('accent', 'category', 'dark', 'colorblind', 'pastel',
+                   'set1', 'set2', 'set3', 'paired')
+
+    reverse = cmap.endswith('_r')
+    ncolors = ncolors or 256
 
     # Alias mpl tab cmaps with bokeh Category cmaps
     if cmap.startswith('tab'):
@@ -506,21 +510,26 @@ def bokeh_palette_to_palette(cmap, ncolors=None):
     if palette is None:
         raise ValueError("Supplied palette %s not found among bokeh palettes" % cmap)
     elif isinstance(palette, dict):
-        if ncolors in palette:
+        if ncolors and ncolors in palette:
             palette = palette[ncolors]
+            if not reverse:
+                # Bokeh palettes are stored in reverse order
+                palette = palette[::-1]
         elif any(cat in cmap.lower() for cat in categorical):
             palette = sorted(palette.items())[-1][1]
         else:
-            palette = sorted(palette.items())[-1][1]
-            palette = polylinear_gradient(palette, ncolors or 256)
+            largest_factor = sorted([n for n in palette if ncolors%(n-1) == 0])[-1]
+            palette = palette[largest_factor]
+            if not reverse:
+                # Bokeh palettes are stored in reverse order
+                palette = palette[::-1]
+            palette = polylinear_gradient(palette, ncolors)
     elif callable(palette):
-        palette = palette(ncolors or 256)
-    if ncolors:
-        return [palette[i%len(palette)] for i in range(ncolors)]
+        palette = palette(ncolors)
     return list(palette)
 
 
-def linear_gradient(start_hex, finish_hex="#FFFFFF", n=10):
+def linear_gradient(start_hex, finish_hex, n=10):
     """
     Interpolates the color gradient between to hex colors
     """
@@ -537,15 +546,15 @@ def polylinear_gradient(colors, n):
     """
     Interpolates the color gradients between a list of hex colors.
     """
-    n_out = int(float(n) / (len(colors) - 1))
+    n_out = int(float(n) / (len(colors)-1))
     gradient = linear_gradient(colors[0], colors[1], n_out)
 
-    if len(colors) <= 1:
+    if len(colors) == len(gradient):
         return gradient
 
     for col in range(1, len(colors) - 1):
-        next_colors = linear_gradient(colors[col], colors[col+1], n_out)
-        gradient += next_colors[1:]
+        next_colors = linear_gradient(colors[col], colors[col+1], n_out+1)
+        gradient += next_colors[1:] if len(next_colors) > 1 else next_colors
     return gradient