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From: Dave Angel <davea@davea.name>
Subject: Re:fseek In Compressed Files
Date: Thu, 30 Jan 2014 06:55:32 -0500 (EST)
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Xref: csiph.com comp.lang.python:64985

 Ayushi Dalmia <ayushidalmia2604@gmail.com> Wrote in message:
> Hello,
> 
> I need to randomly access a bzip2 or gzip file. How can I set the offset for a line and later retreive the line from the file using the offset. Pointers in this direction will help.
> 

Start with the zlib module. Note that it doesn't handle all
 possible compression types, like compress and pack.
 

I don't imagine that seeking to a line in a compressed text file
 would be any easier than a non compressed one. Try using
 gzip.open in a text mode to get a handle,  then loop through it
 line by line.  If you save all the offsets in a list,  you
 should
subsequently be able to seek to a remembered offset. But
 realize it'll be horribly slow,  compared to a non compressed
 one. 

Consider using readlines and referencing the lines from there.  Or
 building a temp file if too big for ram.

If this is not enough,  tell us your Python version and your os, 
 and show what you've tried and what went wrong. 

-- 
DaveA