def copy_rev(s):
    """Takes a string, reverses it and appends it to the back of the original
    string.

    Parameters
    ----------
    s : string
        To be reversed.

    Returns
    -------
    rev_s : string
        `s`, reversed and added to the back of `s`.
    """

    # Initialisations
    reversed_list = [ ]
    s_list = list(s)

    for i in range(len(s)-1, -1, -1):
        reversed_list.append(s[i])
        
    overall_list = s_list + reversed_list
    overall_string = "".join(overall_list)
        
    return overall_string