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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.python
Subject: Step further with filebasedMessages
Organization: Decebal Computing
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Date: Tue, 05 May 2015 10:52:54 +0200
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Xref: csiph.com comp.lang.python:89946

I now defined get_message_slice:
    ### Add step
    def get_message_slice(message_filename, start, end):
        """
        Get a slice of messages, where 0 is the first message
        Works with negative indexes
        The values can be ascending and descending
        """

        message_list    = []
        real_file       = expanduser(message_filename)
        nr_of_messages  = get_nr_of_messages(real_file)
        if start < 0:
            start += nr_of_messages
        if end < 0:
            end += nr_of_messages
        assert (start >= 0) and (start < nr_of_messages)
        assert (end   >= 0) and (end   < nr_of_messages)
        if start > end:
            tmp             = start
            start           = end
            end             = tmp
            need_reverse    = True
        else:
            need_reverse    = False
        with open(real_file, 'r') as f:
            for message in islice(f, start, end + 1):
                message_list.append(message.rstrip())
        if need_reverse:
            message_list.reverse()
        return message_list

Is that a good way?

I also had:
    def get_indexed_message(message_filename, index):
        """
        Get index message from a file, where 0 gets the first message
        A negative index gets messages indexed from the end of the file
        Use get_nr_of_messages to get the number of messages in the file
        """

        real_file       = expanduser(message_filename)
        nr_of_messages  = get_nr_of_messages(real_file)
        if index < 0:
            index += nr_of_messages
        assert (index >= 0) and (index < nr_of_messages)
        with open(real_file, 'r') as f:
            [line] = islice(f, index, index + 1)
            return line.rstrip()

But changed it to:
    def get_indexed_message(message_filename, index):
        """
        Get index message from a file, where 0 gets the first message
        A negative index gets messages indexed from the end of the file
        Use get_nr_of_messages to get the number of messages in the file
        """

        return get_message_slice(message_filename, index, index)[0]

Is that acceptable? I am a proponent of DRY.
Or should I at least keep the assert in it?

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof