Create contrasting color for foreground text and elements

contrast.py

import re

def contrast(basecolor, format='HEX'):
    '''
    Create a contrasting color for foreground text and elements
    Depending on the color [argument], return either black or white hex code
    Useful for automatically coloring text which overlays a background
    Output formats: HEX (hexidecimal) and RGB (as tuple)
    '''
    
    # Validate input
    regex = '^#?([a-f0-9]{6}|[a-f0-9]{3})$'
    if len(re.findall(regex, basecolor)) != 1:
        raise ValueError('Please enter a proper hex color code: #ffffff or #fff')
    else:
        hexcode = basecolor[1:]

    # Split into R,G,B into individual values
    rgb_values = [hexcode[i:i + int(len(hexcode) / 3)] for i in range(0, len(hexcode), int(len(hexcode) / 3))]
    
    # Check for single values and double them: #fff is shorthand for #ffffff
    rgb_values = [i*2 if len(i) == 1 else i for i in rgb_values]
    
    #Convert to decimal
    red = int(rgb_values[0], 16)
    green = int(rgb_values[1], 16)
    blue = int(rgb_values[2], 16)

    # Calculate luminance
    luminance = float((0.299 * red + 0.587 * green + 0.114 * blue)/255)

    # Calculate d (darkness) value
    if luminance > 0.5:
        d = 0
    else:
        d = 255

    # Convert darkness value to hex value and create hex color code or RGB tuple
    if format == 'HEX':
        return f'#{d:X}{d:X}{d:X}'
    else: # format = RGB
        return (d, d, d)

Use Case:
Solid desktop background (wallpaper) changes from light to dark, or vice versa, on a regular basis. This can cause issues reading text displayed on Desktop (conky, rainmeter, etc.). This script will create a contrasting color hex code to standout from that wallpaper for readability.