Asserts a provided string is a valid duration token representation

    :param  token: duration representation token
    :type   token: string

def valid_token(token):
    """Asserts a provided string is a valid duration token representation

    :param  token: duration representation token
    :type   token: string
    """
    is_scale = False

    # Check if the token represents a scale
    # If it doesn't set a flag accordingly
    try:
        Scale(token)
        is_scale = True
    except ScaleFormatError:
        pass

    # If token either represents a numerical value, a
    # separator token, or a scale, it is considered valid
    if any([token.isdigit(), token in SEPARATOR_TOKENS, is_scale]):
        return True

    return False