Merge branch 'master' into colorscale-sampling

# Conflicts:
#	packages/python/plotly/_plotly_utils/colors/__init__.py
#	packages/python/plotly/plotly/tests/test_core/test_colors/test_colors.py

Author: CarlAndersson

Diff for: packages/python/plotly/_plotly_utils/colors/__init__.py

@@ -808,6 +808,33 @@ def named_colorscales():
     return [c for c in ColorscaleValidator("", "").named_colorscales]
 
 
+def get_colorscale(name):
+    """
+    Returns the colorscale for a given name. See `named_colorscales` for the
+    built-in colorscales.
+    """
+    from _plotly_utils.basevalidators import ColorscaleValidator
+
+    if not isinstance(name, str):
+        raise exceptions.PlotlyError("Name argument have to be a string.")
+
+    name = name.lower()
+    if name[-2:] == "_r":
+        should_reverse = True
+        name = name[:-2]
+    else:
+        should_reverse = False
+
+    if name in ColorscaleValidator("", "").named_colorscales:
+        colorscale = ColorscaleValidator("", "").named_colorscales[name]
+    else:
+        raise exceptions.PlotlyError(f"Colorscale {name} is not a built-in scale.")
+
+    if should_reverse:
+        return colorscale[::-1]
+    return colorscale
+
+
 def sample_colorscale(colorscale, samplepoints, low=0.0, high=1.0, colortype="rgb"):
     """
     Samples a colorscale at specific points.

Diff for: packages/python/plotly/plotly/colors/__init__.py

@@ -46,4 +46,5 @@
     "plotlyjs",
     "DEFAULT_PLOTLY_COLORS",
     "PLOTLY_SCALES",
+    "get_colorscale",
 ]

Diff for: packages/python/plotly/plotly/io/_html.py

@@ -423,11 +423,6 @@ def write_html(
         require an active internet connection in order to load the plotly.js
         library.
 
-        If 'directory', a script tag is included that references an external
-        plotly.min.js bundle that is assumed to reside in the same
-        directory as the HTML file. If `file` is a string to a local file path
-        and `full_html` is True then
-
         If 'directory', a script tag is included that references an external
         plotly.min.js bundle that is assumed to reside in the same
         directory as the HTML file.  If `file` is a string to a local file

Diff for: packages/python/plotly/plotly/tests/test_core/test_colors/test_colors.py

@@ -138,6 +138,32 @@ def test_make_colorscale(self):
             PlotlyError, pattern2, colors.make_colorscale, color_list2, scale
         )
 
+    def test_get_colorscale(self):
+
+        # test for incorrect input type
+        pattern = "Name argument have to be a string."
+        name = colors.sequential.haline
+
+        self.assertRaisesRegexp(PlotlyError, pattern, colors.get_colorscale, name)
+
+        # test for non-existing colorscale
+        pattern = r"Colorscale \S+ is not a built-in scale."
+        name = "foo"
+        self.assertRaisesRegex(PlotlyError, pattern, colors.get_colorscale, name)
+
+        # test non-capitalised access
+        self.assertEqual(colors.sequential.haline, colors.get_colorscale("haline"))
+        # test capitalised access
+        self.assertEqual(colors.diverging.Earth, colors.get_colorscale("Earth"))
+        # test accessing non-capitalised scale with capitalised name
+        self.assertEqual(colors.cyclical.mrybm, colors.get_colorscale("Mrybm"))
+        # test accessing capitalised scale with non-capitalised name
+        self.assertEqual(colors.sequential.Viridis, colors.get_colorscale("viridis"))
+        # test accessing reversed scale
+        self.assertEqual(
+            colors.diverging.Portland_r, colors.get_colorscale("portland_r")
+        )
+
     def test_sample_colorscale(self):
 
         # test that sampling a colorscale at the defined points returns the same