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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 uri(host='localhost', port=5432, dbname='postgres', user='postgres', password=None):
 """Return a PostgreSQL connection URI for the specified values. :param str host: Host to connect to :param int port: Port to connect on :param str dbname: The database name :param str user: User to connect as :param str password: The password to use, None for no password :return str: The PostgreSQL connection URI """

    if port:
        host = '%s:%s' % (host, port)
    if password:
        return 'postgresql://%s:%s@%s/%s' % (user, password, host, dbname)
    return 'postgresql://%s@%s/%s' % (user, host, dbname)