Default to #rrggbb, not #rrggbbaa.

Author: anntzer

doc/users/colors.rst

@@ -9,7 +9,7 @@ it can be provided as:
 
 * ``(r, g, b)`` tuples
 * ``(r, g, b, a)`` tuples
-* hex string, ex ``#OFOFOF``
+* hex string, ex ``#0F0F0F``, or ``#0F0F0F0F`` (with alpha channel)
 * float value between [0, 1] for gray level
 * One of ``{'b', 'g', 'r', 'c', 'm', 'y', 'k', 'w'}``
 * valid CSS4/X11 color names

lib/matplotlib/colors.py

@@ -18,7 +18,7 @@
 The module also provides functions for checking whether an object can be
 interpreted as a color (:func:`is_color_like`), for converting such an object
 to an RGBA tuple (:func:`to_rgba`) or to an HTML-like hex string in the
-`#rrggbbaa` format (:func:`to_hex`), and a sequence of colors to an `(n, 4)`
+`#rrggbb` format (:func:`to_hex`), and a sequence of colors to an `(n, 4)`
 RGBA array (:func:`to_rgba_array`).  Caching is used for efficiency.
 
 Commands which take color arguments can use several formats to specify
@@ -240,13 +240,17 @@ def to_rgb(c):
     return to_rgba(c)[:3]
 
 
-def to_hex(c, alpha=None):
+def to_hex(c, keep_alpha=False):
     """Convert `c` to a hex color.
 
-    If `alpha` is not `None`, it forces the alpha value.
+    Uses the #rrggbb format if `keep_alpha` is False (the default), `#rrggbbaa`
+    otherwise.
     """
+    c = to_rgba(c)
+    if not keep_alpha:
+        c = c[:3]
     return "#" + "".join(format(int(np.round(val * 255)), "02x")
-                         for val in to_rgba(c, alpha=alpha))
+                         for val in c)
 
 
 ### Backwards-compatible color-conversion API
@@ -258,7 +262,7 @@ def to_hex(c, alpha=None):
 
 def rgb2hex(c):
     'Given an rgb or rgba sequence of 0-1 floats, return the hex string'
-    return to_hex(c)[:7]  # Drop alpha.
+    return to_hex(c)
 
 
 def hex2color(c):

lib/matplotlib/tests/test_colors.py

@@ -555,8 +555,8 @@ def angled_plane(azimuth, elevation, angle, x, y):
 
 
 def test_xkcd():
-    assert mcolors.to_hex("blue") == "#0000ffff"
-    assert mcolors.to_hex("xkcd:blue") == "#0343dfff"
+    assert mcolors.to_hex("blue") == "#0000ff"
+    assert mcolors.to_hex("xkcd:blue") == "#0343df"
 
 
 def _sph2cart(theta, phi):
@@ -607,8 +607,8 @@ def test_colormap_reversing():
 def test_cn():
     matplotlib.rcParams['axes.prop_cycle'] = cycler('color',
                                                     ['blue', 'r'])
-    assert mcolors.to_hex("C0") == '#0000ffff'
-    assert mcolors.to_hex("C1") == '#ff0000ff'
+    assert mcolors.to_hex("C0") == '#0000ff'
+    assert mcolors.to_hex("C1") == '#ff0000'
 
     matplotlib.rcParams['axes.prop_cycle'] = cycler('color',
                                                     ['xkcd:blue', 'r'])
@@ -622,10 +622,11 @@ def test_conversions():
     # alpha is properly set.
     assert_equal(mcolors.to_rgba((1, 1, 1), .5), (1, 1, 1, .5))
     # builtin round differs between py2 and py3.
-    assert_equal(mcolors.to_hex((.7, .7, .7)), "#b2b2b2ff")
+    assert_equal(mcolors.to_hex((.7, .7, .7)), "#b2b2b2")
     # hex roundtrip.
     hex_color = "#1234abcd"
-    assert_equal(mcolors.to_hex(mcolors.to_rgba(hex_color)), hex_color)
+    assert_equal(mcolors.to_hex(mcolors.to_rgba(hex_color), keep_alpha=True),
+                 hex_color)
 
 
 if __name__ == '__main__':