[Python-ideas] Marvelous movable memoryview

[Antoine Pitrou]

On Thu, 26 Jul 2012 18:40:33 -0400
Matt Chaput <matt at whoosh.ca> wrote:
> By which I mean a memoryview that lets you change the start and end 
> offsets of its view of the underlying object (not modifying the 
> underlying object).
> 
> Let's say I want to slice a long string s into trigrams and write them 
> to disk (or something).
> 
>    for i in xrange(0, len(s) - 3):
>        x = s[i:i + 3]
>        myfile.write(x)
> 
> At each step the slice copies the bytes of the string, even though all I 
> do is write them to disk.

To be honest, copying three bytes is a trivial operation compared to
all the rest (interpreting bytecode, instantiating and destructing
bytes objects, calling I/O routines, etc.).

> Shouldn't I be able to do this?
> 
>    m = memoryview(s)
>    for i in xrange(0, len(s) - 3):
>        m.start = i
>        m.end = i + 3
>        myfile.write(m)

You wouldn't win anything over the simple bytes slicing approach, IMO.
(even with PyPy or another interpreter)

Regards

Antoine.


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