[Patches] [ python-Patches-1677872 ] Efficient reverse line iterator

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Patches item #1677872, was opened at 2007-03-10 08:47
Message generated for change (Comment added) made by rhettinger
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Category: Library (Lib)
Group: Python 3000
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Mark Russell (mark_t_russell)
Assigned to: Nobody/Anonymous (nobody)
Summary: Efficient reverse line iterator 

Initial Comment:
This is an implementation of __reversed__ for the TextIOWrapper type from the new IO interface (see http://docs.google.com/Doc?id=dfksfvqd_1cn5g5m).  It is used as:

    import io
    for line in reversed(io.open(filename)):
          ...

It is efficient (only reads a block at a time) but can handle arbitrary length lines.  It is useful for scanning backwards through big log files, but my main reason for submitting it is as a demonstration of the usefulness of the new IO layers - it works by putting a new buffering layer round the RawIOBase object from the open() call.

It's just a proof of concept, but if there's interest in this I'm happy to write unit tests and documentation.

The patch also makes io.BufferedReader support buffering, and adds a very minimal implementation of io.TextIOBase and io.TextIOWrapper (needed to make io.open() work).



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>Comment By: Raymond Hettinger (rhettinger)
Date: 2007-04-11 12:40

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FWIW, I've wanted something like this for a long time (for scanning log
files in reverse).

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