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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 fmt_routes(bottle_app):
 """Return a pretty formatted string of the list of routes."""

    routes = [(r.method, r.rule) for r in bottle_app.routes]
    if not routes:
        return
    string = 'Routes:\n'
    string += fmt_pairs(routes, sort_key=operator.itemgetter(1))
    return string