Unable to parse 3-digit RGB string

[omgraae]

Issue Description

Problem

The method from_string in the RGBColor class was failing when an invalid RGB hex string was passed. Specifically, the method expected a 6-digit hex string but did not handle cases where a 3-digit hex string was provided, leading to a ValueError when attempting to convert an empty string to an integer.

Background

I am using pygments to perform syntax highlighting on source-code. For reasons, the color-codes are ?sometimes? in a 3-digit format. To fix my immediate issue, I selected to alter the class rather than validating and/or translating input before calling it. I have only seen the 3-digit HEX codes in my project, but did consider issues from other types of colour coding from arbitrary input. Probably an elegant way exists to translate something like the 3-digit hex or even color names:
w3schools colors names

A solution

The method was updated locally on my computer to handle both 6-digit and 3-digit RGB hex strings. The updated method uses regular expressions to validate the input string and appropriately converts 3-digit hex strings by duplicating each digit.

Code Changes

file: shared.py

import re

Class: RGBColor

    @classmethod
    def from_string(cls, rgb_hex_str: str) -> RGBColor:
        """Return a new instance from an RGB color hex string like ``'3C2F80'`` or like ``'1FC'``."""
        if re.match(r"^[0-9a-fA-F]{6}$", rgb_hex_str):
            r = int(rgb_hex_str[:2], 16)
            g = int(rgb_hex_str[2:4], 16)
            b = int(rgb_hex_str[4:], 16)
        elif re.match(r"^[0-9a-fA-F]{3}$", rgb_hex_str):
            """Correct translation into 6 digit hex codes is doubling every digit."""
            r = int(rgb_hex_str[0] * 2, 16)
            g = int(rgb_hex_str[1] * 2, 16)
            b = int(rgb_hex_str[2] * 2, 16)
        else:
            raise ValueError(f"Invalid RGB hex string: {rgb_hex_str}")
        return cls(r, g, b)

[omgraae]

python-docx_v1.1.2_rgb.patch

Apply with:

patch .venv/lib/python*/site-packages/docx/shared.py < python-docx_v1.1.2_rgb.patch
`