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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 increment(key, delta=1, host=DEFAULT_HOST, port=DEFAULT_PORT):
    '''
    Increment the value of a key

    CLI Example:

    .. code-block:: bash

        salt '*' memcached.increment <key>
        salt '*' memcached.increment <key> 2
    '''
    conn = _connect(host, port)
    _check_stats(conn)
    cur = get(key)

    if cur is None:
        raise CommandExecutionError('Key \'{0}\' does not exist'.format(key))
    elif not isinstance(cur, six.integer_types):
        raise CommandExecutionError(
            'Value for key \'{0}\' must be an integer to be '
            'incremented'.format(key)
        )

    try:
        return conn.incr(key, delta)
    except ValueError:
        raise SaltInvocationError('Delta value must be an integer')