impl/python/hex_encode.py

from typing import Sequence

_DIGITS = "0123456789abcdef"


def hex_encode(bytes: Sequence[int]) -> str:
    """Bytes as lowercase hexadecimal, two digits per byte.

    Bytes are a list of integers 0-255 across the registry (there is no bytes
    type); a Python ``bytes`` value is such a sequence and is accepted as is.
    A value outside the range is refused rather than masked to a byte.
    """
    if isinstance(bytes, (str, dict)) or not hasattr(bytes, "__len__"):
        raise TypeError("bytes must be a list of integers from 0 to 255")
    out = []
    for b in bytes:
        # bool is an int in Python; true is not a byte in the other two languages.
        if type(b) is not int or b < 0 or b > 255:
            raise ValueError("bytes must be a list of integers from 0 to 255")
        out.append(_DIGITS[b >> 4] + _DIGITS[b & 15])
    return "".join(out)