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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getUsers(context, roles, allow_empty=True):
 """ Present a DisplayList containing users in the specified list of roles """

    mtool = getToolByName(context, 'portal_membership')
    pairs = allow_empty and [['', '']] or []
    users = mtool.searchForMembers(roles=roles)
    for user in users:
        uid = user.getId()
        fullname = user.getProperty('fullname')
        if not fullname:
            fullname = uid
        pairs.append((uid, fullname))
    pairs.sort(lambda x, y: cmp(x[1], y[1]))
    return DisplayList(pairs)