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Update for checking whether colors have an alpha channel #27327

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Merged
rcomer merged 16 commits into from
Jan 6, 2025
Merged

Update for checking whether colors have an alpha channel #27327

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0586383
Update _has_alpha_channel
landoskape Nov 15, 2023
9719b60
Update lib/matplotlib/colors.py
landoskape Nov 15, 2023
77e759f
Clarify comment explanation
landoskape Nov 15, 2023
5d7edca
Remove unnecessary check about is_color_like
landoskape Nov 21, 2023
e7220c8
update docstring for undefined case
landoskape Jan 3, 2025
0cf3612
Deprecate unused method
landoskape Jan 3, 2025
e2099e6
Remove unnecessary method
landoskape Jan 4, 2025
5ac2c0f
Flake formatting update
landoskape Jan 4, 2025
212363e
Don't specify what an undefined result does
landoskape Jan 4, 2025
73127eb
Recursive check which handles hex colors too
landoskape Jan 4, 2025
c3cf8d4
Whitespace
landoskape Jan 4, 2025
b81786c
Remove is_color_like check and explain
landoskape Jan 5, 2025
80d422d
Don't discuss undefined results
landoskape Jan 5, 2025
bbe6fa2
Remove test of undefined result
landoskape Jan 5, 2025
de5e42d
Spelling error
landoskape Jan 6, 2025
0813e13
improved grammar in comment
landoskape Jan 6, 2025
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32 changes: 30 additions & 2 deletions lib/matplotlib/colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -233,8 +233,36 @@ def is_color_like(c):

def _has_alpha_channel(c):
"""Return whether *c* is a color with an alpha channel."""
# 4-element sequences are interpreted as r, g, b, a
return not isinstance(c, str) and len(c) == 4
# If c is not a color, it doesn't have an alpha channel
if not is_color_like(c):
return False

@oscargus oscargus Nov 15, 2023

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One should probably check the code if this has already been called. Since this is a private method one can require that it is checked.

@landoskape landoskape Nov 15, 2023

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Hm, I'm sure I know how to do that or what you mean. Would you explain a little more?

(also, thanks for the comments, as always)


# if c is a hex, it has an alpha channel when it has 4 (or 8) digits after '#'
if isinstance(c, str) and c[0] == '#' and (len(c) == 5 or len(c) == 9):
# example: '#fff8' or '#0f0f0f80'
return True

# if c isn't a string, it can be an RGB(A) or a color-alpha tuple
if not isinstance(c, str):
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# if it has length 4, it has an alpha channel
if len(c) == 4:
# example: [0.5, 0.5, 0.5, 0.5]
return True

# if it has length 2, the 2nd element isn't None, and the 1st element has len=3
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if len(c) == 2 and (c[1] is not None or len(c[0]) == 4):
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# example: ([0.5, 0.5, 0.5, 0.5], None) or ('r', 0.5)
return True

# otherwise it doesn't have an alpha channel
return False


def _has_alpha_channel_array(cseq):

@timhoffm timhoffm Oct 7, 2024

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This is not used anywhere right now. Therefore, we don't need it here.

@landoskape landoskape Jan 3, 2025

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It is now deprecated (I added the standard _api.deprecated decorator). In addition I added a deprecation file in the doc/ folder.

@timhoffm timhoffm Jan 4, 2025

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Um, you've just introduced this function and immediately deprecated it?!? You should simply not add it to the PR.

"""Return whether each element in *cseq* is a color with an alpha channel"""
if is_color_like(cseq):
cseq = [cseq] # force it to be a sequence
return [_has_alpha_channel(c) for c in cseq]


def _check_color_like(**kwargs):
Expand Down
9 changes: 9 additions & 0 deletions lib/matplotlib/tests/test_colors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1231,10 +1231,19 @@ def test_colormap_reversing(name):
def test_has_alpha_channel():
assert mcolors._has_alpha_channel((0, 0, 0, 0))
assert mcolors._has_alpha_channel([1, 1, 1, 1])
assert mcolors._has_alpha_channel('#fff8')
assert mcolors._has_alpha_channel('#0f0f0f80')
assert mcolors._has_alpha_channel(('r', 0.5))
assert mcolors._has_alpha_channel(([1, 1, 1, 1], None))
assert not mcolors._has_alpha_channel('blue') # 4-char string!
assert not mcolors._has_alpha_channel('0.25')
assert not mcolors._has_alpha_channel('r')
assert not mcolors._has_alpha_channel((1, 0, 0))
assert not mcolors._has_alpha_channel('#fff')
assert not mcolors._has_alpha_channel('#0f0f0f')
assert not mcolors._has_alpha_channel(('r', None))
assert not mcolors._has_alpha_channel(([1, 1, 1], None))
assert not mcolors._has_alpha_channel(1) # non-colors don't have alpha channels
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def test_cn():
Expand Down