import hashlib


def get_digest(value):
    """
    Returns a hashlib digest algorithm from a string
    """
    if not isinstance(value,str):
        return value
    value = value.lower()
    if value == "md5":
        return hashlib.md5
    elif value == "sha1":
        return hashlib.sha1
    elif value == "sha224":
        return hashlib.sha224
    elif value == "sha256":
        return hashlib.sha256
    elif value == "sha384":
        return hashlib.sha384
    elif value == "sha512":
        return hashlib.sha512
    else:
        raise ValueError("Invalid digest algorithm")