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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 list_roles():
 """Show a list of all available roles"""

    for role in lib.get_roles():
        margin_left = lib.get_margin(len(role['fullname']))
        print("{0}{1}{2}".format(
            role['fullname'], margin_left,
            role.get('description', '(no description)')))