colours.py

def hex_to_RGB(hex):
    ''' "#FFFFFF" -> [255,255,255] '''
    # Pass 16 to the integer function for change of base
    return [int(hex[i:i+2], 16) for i in range(1, 6, 2)]


def RGB_to_hex(RGB):
    ''' [255,255,255] -> "#FFFFFF" '''
    # Components need to be integers for hex to make sense
    RGB = [int(x) for x in RGB]
    return "#"+"".join(["0{0:x}".format(v) if v < 16 else
                        "{0:x}".format(v) for v in RGB])


def color_dict(gradient):
    ''' Takes in a list of RGB sub-lists and returns dictionary of
      colors in RGB and hex form for use in a graphing function
      defined later on '''
    return {"hex": [RGB_to_hex(RGB) for RGB in gradient],
            "r": [RGB[0] for RGB in gradient],
            "g": [RGB[1] for RGB in gradient],
            "b": [RGB[2] for RGB in gradient]}


def linear_gradient(start_hex, finish_hex="#FFFFFF", n=10):
    ''' returns a gradient list of (n) colors between
      two hex colors. start_hex and finish_hex
      should be the full six-digit color string,
      inlcuding the number sign ("#FFFFFF") '''
    # Starting and ending colors in RGB form
    s = hex_to_RGB(start_hex)
    f = hex_to_RGB(finish_hex)
    # Initilize a list of the output colors with the starting color
    RGB_list = [s]
    # Calcuate a color at each evenly spaced value of t from 1 to n
    for t in range(1, n):
        # Interpolate RGB vector for color at the current value of t
        curr_vector = [
            int(s[j] + (float(t)/(n-1))*(f[j]-s[j]))
            for j in range(3)
        ]
        # Add it to our list of output colors
        RGB_list.append(curr_vector)

    return color_dict(RGB_list)