[Numpy-discussion] memmap & dtype issue

Travis E. Oliphant oliphant@enthought....
Mon Dec 1 08:30:02 CST 2008

Wim Bakker wrote:
> For a long time now, numpy's memmap has me puzzled by its behavior. When I use
> memmap straightforward on a file it seems to work fine, but whenever I try to 
> do a memmap using a dtype it seems to gobble up the whole file into memory. 
I don't understand your question.  From my experience, the memmap is 
working fine.   Please post and example that illustrates your point.
> This, of course, makes the use of memmap futile. I would expect that the 
> result of such an operation would give me a true memmap and that the data 
> would be converted to dtype on the fly.
There is no conversion on the fly when you use memmap.   You construct 
an array of the same data-type as is in the file and then manipulate 
portions of it as needed.
> Am I doing something wrong? Are my expectations wrong?
My guess is that your expectations are not accurate, but example code 
would help sort it out.

Best regards,


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