pieces = [1, 2, 5, 10, 20, 50, 100, 200]

def rendu_monnaie(somme_due, somme_versee):

    rendu = ...
    a_rendre = ...
    i = len(pieces) - 1
    while ... :
        if pieces[i] <= a_rendre :
            rendu.append(...)
            a_rendre = ...
        else :
            i = ...
    return rendu