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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 get_users_by_roles(roles=None):
 """Search Plone users by their roles :param roles: Plone role name or list of roles :type roles: list/str :returns: List of Plone users having the role(s) """

    if not isinstance(roles, (tuple, list)):
        roles = [roles]
    mtool = get_tool("portal_membership")
    return mtool.searchForMembers(roles=roles)