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Small refactor of color utils for readibility and type checkability #55

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Apr 18, 2024
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Small refactor of color utils for readibility and type checkability #55

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61 changes: 40 additions & 21 deletions a11y_pygments/utils/wcag_contrast.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,35 +6,56 @@
from typing import NewType, Tuple, TypeAlias, Union


# float01 is a float greater than or equal to 0 and less than or equal to 1
float01 = NewType("float01", float)
RGBColor: TypeAlias = Tuple[float01, float01, float01]


def xx_01(xx: str) -> float01:
"""Convert an 8-bit hex value to a float between 0 and 1.

>>> xx_01("00")
0.0
>>> xx_01("33")
0.2
>>> xx_01("55")
0.3333333333333333
>>> xx_01("cc")
0.8
>>> xx_01("ff")
1.0
"""
return float01(int(xx, 16) / 255)


def hex_to_rgb01(hex: str) -> RGBColor:
"""Convert a hex defined colour to RGB.

Args:
hex (string): color in hex format (#rrggbb/#rgb)

Returns:
rgb: tuple of rgb values ``(r, g, b)``, where each channel (red, green, blue,
alpha) can assume values between 0 and 1.
rgb: tuple of rgb values ``(r, g, b)``, where each channel (red, green,
blue) can assume values between 0 and 1 (inclusive).
"""
# hex color in #rrggbb format
match = re.match(r"\A#[a-fA-F0-9]{6}\Z", hex)
if match:
res = tuple(float01(int(n, 16) / 255) for n in [hex[1:3], hex[3:5], hex[5:7]])
assert len(res) == 3, "please type checker with length of tuple"
return res
# hex color in #rgb format, shorthand for #rrggbb.
match = re.match(r"\A#[a-fA-F0-9]{3}\Z", hex)
if match:
res = tuple(
float01(int(n, 16) / 255) for n in [hex[1] * 2, hex[2] * 2, hex[3] * 2]

if re.match(r"\A#[a-fA-F0-9]{6}\Z", hex):
# Full hex color (#rrggbb) format
return (
xx_01(hex[1:3]),
xx_01(hex[3:5]),
xx_01(hex[5:7]),
)
assert len(res) == 3, "please type checker with length of tuple"
return res
assert False, "please type checker with unreachable end"

if re.match(r"\A#[a-fA-F0-9]{3}\Z", hex):
# Short hex color (#rgb) format, shorthand for #rrggbb
return (
xx_01(hex[1] * 2),
xx_01(hex[2] * 2),
xx_01(hex[3] * 2),
)

raise ValueError("Invalid hex color format")


def sRGB_channel(v: float01) -> float:
Expand Down Expand Up @@ -92,7 +113,7 @@ def contrast_ratio(color1: RGBColor, color2: RGBColor) -> float:

def passes_contrast(
color1: RGBColor, color2: RGBColor, level="AA"
) -> Union[bool, float, None]:
) -> Union[bool, float]:
"""Method to verify the contrast ratio between two colours.

Args:
Expand All @@ -101,9 +122,6 @@ def passes_contrast(
level (str, optional): WCAG contrast level. Defaults to "AA".
"""

if level not in ["AA", "AAA"]:
raise ValueError("level must be either 'AA' or 'AAA'")

ratio = contrast_ratio(color1, color2)

if level == "AA":
Expand All @@ -116,7 +134,8 @@ def passes_contrast(
return round(ratio, 2)
else:
return False
return None

raise ValueError("level must be either 'AA' or 'AAA'")


def get_wcag_level_normal_text(contrast: float) -> str:
Expand Down
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