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    <p>This may be quicker than yours. Makes no assumptions about line length. Backs through the file one block at a time till it's found the right number of '\n' characters.</p> <pre><code>def tail( f, lines=20 ): total_lines_wanted = lines BLOCK_SIZE = 1024 f.seek(0, 2) block_end_byte = f.tell() lines_to_go = total_lines_wanted block_number = -1 blocks = [] # blocks of size BLOCK_SIZE, in reverse order starting # from the end of the file while lines_to_go &gt; 0 and block_end_byte &gt; 0: if (block_end_byte - BLOCK_SIZE &gt; 0): # read the last block we haven't yet read f.seek(block_number*BLOCK_SIZE, 2) blocks.append(f.read(BLOCK_SIZE)) else: # file too small, start from begining f.seek(0,0) # only read what was not read blocks.append(f.read(block_end_byte)) lines_found = blocks[-1].count('\n') lines_to_go -= lines_found block_end_byte -= BLOCK_SIZE block_number -= 1 all_read_text = ''.join(reversed(blocks)) return '\n'.join(all_read_text.splitlines()[-total_lines_wanted:]) </code></pre> <p>I don't like tricky assumptions about line length when -- as a practical matter -- you can never know things like that.</p> <p>Generally, this will locate the last 20 lines on the first or second pass through the loop. If your 74 character thing is actually accurate, you make the block size 2048 and you'll tail 20 lines almost immediately.</p> <p>Also, I don't burn a lot of brain calories trying to finesse alignment with physical OS blocks. Using these high-level I/O packages, I doubt you'll see any performance consequence of trying to align on OS block boundaries. If you use lower-level I/O, then you might see a speedup.</p>
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    1. POGet last n lines of a file with Python, similar to tail
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    1. USMark Amery
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    1. CONice. At least one poster that read the question and the code in there :)
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      1. USArmin Ronacher
    2. COThis works really well. I just pulled it into a script to read the last 4000 lines of a log file before I parse them. It works quickly and makes sense. Thanks!
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      1. USJeff Hellman
    3. COThis fails on small logfiles -- IOError: invalid argument -- f.seek( block*1024, 2 )
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      1. USohnoes
 

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