fix late binding and proper reversal for funcs (#296)

Author: cvanelteren

ultraplot/colors.py

@@ -1271,16 +1271,17 @@ def reversed(self, name=None, **kwargs):
         --------
         matplotlib.colors.LinearSegmentedColormap.reversed
         """
+
         # Reverse segments
+        def _reverse_data(data):
+            if callable(data):
+                return lambda x, func=data: func(1 - x)
+            else:
+                return [(1.0 - x, y1, y0) for x, y0, y1 in reversed(data)]
+
         segmentdata = {
-            key: (
-                (lambda x, func=data: func(x))
-                if callable(data)
-                else [(1.0 - x, y1, y0) for x, y0, y1 in reversed(data)]
-            )
-            for key, data in self._segmentdata.items()
+            key: _reverse_data(data) for key, data in self._segmentdata.items()
         }
-
         # Reverse gammas
         if name is None:
             name = self._make_name(suffix="r")
@@ -3137,7 +3138,7 @@ def _translate_key(self, original_key, mirror=True):
         # Handle reversal
         reverse = key.endswith("_r")
         if reverse:
-            key = key.rstrip("_r")
+            key = key.removesuffix("_r")
 
         # Check if the key exists in builtin colormaps
         if self._has_item(key):
@@ -3156,7 +3157,7 @@ def _translate_key(self, original_key, mirror=True):
 
             # Try mirroring the non-lowered key
             if reverse:
-                original_key = original_key.strip("_r")
+                original_key = original_key.removesuffix("_r")
             half = len(original_key) // 2
             mirrored_key = original_key[half:] + original_key[:half]
             if self._has_item(mirrored_key):
@@ -3182,11 +3183,11 @@ def __getitem__(self, key):
         key = self._translate_key(key, mirror=True)
         shift = key.endswith("_s") and not self._has_item(key)
         if shift:
-            key = key.rstrip("_s")
+            key = key.removesuffix("_s")
         reverse = key.endswith("_r") and not self._has_item(key)
 
         if reverse:
-            key = key.rstrip("_r")
+            key = key.removesuffix("_r")
         # Retrieve colormap
         if self._has_item(key):
             value = self._cmaps[key].copy()

ultraplot/tests/test_colormap.py

@@ -0,0 +1,12 @@
+import ultraplot as uplt, pytest, numpy as np
+
+
+def test_colormap_reversal():
+    # Rainbow uses a callable which went wrong see
+    # https://github.com/Ultraplot/UltraPlot/issues/294#issuecomment-3016653770
+    cmap = uplt.Colormap("rainbow")
+    cmap_r = cmap.reversed()
+    for i in range(256):
+        assert np.allclose(
+            cmap(i), cmap_r(255 - i)
+        ), f"Reversed colormap mismatch at index {i}"