[Numpy-discussion] Non-writeable default for numpy.ndarray

Travis Oliphant oliphant.travis at ieee.org
Fri Sep 29 11:55:25 CDT 2006

Tim Hochberg wrote:
> Francesc Altet wrote:
> It's not that the it's being built from ndarray, it's that the buffer 
> that you are passing it is read only. 
This is correct.
> In fact, I'd argue that allowing 
> the writeable flag to be set to True in this case is actually a bug. 
It's actually intentional.  Strings used as buffers are allowed to be 
writeable.  This is an explicit design decision to allow pickles to load 
without making 2 copies of the memory.   The pickled string that Python 
creates is used as the actual memory for loaded arrays.

Now, I suppose it would be possible to still allow this but be more 
finnicky about when a string-used-as-the-memory can be set writeable 
(i.e. we are the only reference to it).  But, this would be a fragile 
solution as well. 

My inclination is to just warn users not to use strings as buffers 
unless they know what they are doing.  The fact that it is read-only by 
default is enough of a guard against "accidentally" altering a string 
you didn't want to alter.


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