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Efficient multi-slicing technique?

MRAB google at mrabarnett.plus.com
Sun Jan 25 14:12:29 EST 2009 
python at bdurham.com wrote:
> Is there an efficient way to multi-slice a fixed with string into 
> individual fields that's logically equivalent to the way one would slice 
> a delimited string using .split()?
> 
> Background: I'm parsing some very large, fixed line-width text files 
> that have weekly columns of data (52 data columns plus related data). My 
> current strategy is to loop through a list of slice()'s to build a list 
> of the specific field values for each line. This is fine for small 
> files, but seems inefficient. I'm hoping that there's a built-in (C 
> based) or 3rd party module that is specifically designed for doing 
> multiple field extractions at once.
> 
You could try the struct module:

 >>> import struct
 >>> struct.unpack("3s4s1s", b"123abcdX")
('123', 'abcd', 'X')
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