8000 Make ListedColormap.monochrome a property · matplotlib/matplotlib@5827742 · GitHub
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timhoffmtimhoffm
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Make ListedColormap.monochrome a property
The calculated property replaces the attribute *monochome*, which was manually set on `__init__`, but was not correctly set for all possible inputs. This property ensures consistency and simplifies initialization at the cost of some computation overhead to determine whether the colormap is monochrome. The computation cost is bearable (even without caching), because it's only used in `ContourSet._process_colors`. It's a separate discussion whether we need this property on colormaps at all (at least as public API). Usually, colormaps are not monochrome and monochrome colormaps are a very special edge case used in contours only. We may eventually deprecate it, but since it is currently public API, let's leave it for now. There's also a technical API incompatibility in that users cannot set the attribute anymore, but I'd argue that that has never been intended and there's no practical use-case, so I refrain from the extra hassle of allowing setting this property.
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‎lib/matplotlib/colors.py

Lines changed: 18 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1191,17 +1191,13 @@ class ListedColormap(Colormap):
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the list will be extended by repetition.
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"""
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def __init__(self, colors, name='from_list', N=None):
1194-
self.monochrome = False # Are all colors identical? (for contour.py)
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if N is None:
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self.colors = colors
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N = len(colors)
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else:
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if isinstance(colors, str):
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self.colors = [colors] * N
1201-
self.monochrome = True
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elif np.iterable(colors):
1203-
if len(colors) == 1:
1204-
self.monochrome = True
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self.colors = list(
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itertools.islice(itertools.cycle(colors), N))
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else:
@@ -1211,7 +1207,6 @@ def __init__(self, colors, name='from_list', N=None):
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pass
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else:
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self.colors = [gray] * N
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self.monochrome = True
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super().__init__(name, N)
1216121 10000 1

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def _init(self):
@@ -1220,6 +1215,24 @@ def _init(self):
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self._isinit = True
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self._set_extremes()
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@property
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def monochrome(self):
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"""Return whether all colors in the colormap are identical."""
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# Replacement for the attribute *monochrome*. This ensures a consistent
1222+
# response independent of the way the ListedColormap was created, which
1223+
# was not the case for the manually set attribute.
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#
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# TODO: It's a separate discussion whether we need this property on
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# colormaps at all (at least as public API). It's a very special edge
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# case and we only use it for contours internally.
1228+
if not self._isinit:
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self._init()
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1231+
N = len(self._lut) - 3 # disregard over / under / bad
1232+
if N <= 1:
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return True
1234+
return np.all(self._lut[0] == self._lut[1:N])
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def resampled(self, lutsize):
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"""Return a new colormap with *lutsize* entries."""
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colors = self(np.linspace(0, 1, lutsize))

‎lib/matplotlib/tests/test_colors.py

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -74,6 +74,12 @@ def test_resampled():
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assert_array_almost_equal(lc(np.nan), lc3(np.nan))
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def test_monochrome():
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assert mcolors.ListedColormap(["red"]).monochrome
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assert mcolors.ListedColormap(["red"] * 5).monochrome
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assert not mcolors.ListedColormap(["red", "green"]).monochrome
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82+
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def test_colormaps_get_cmap():
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cr = mpl.colormaps
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