[Numpy-discussion] immutable arrays

Martin Wiechert Martin.Wiechert at mpimf-heidelberg.mpg.de
Thu Sep 21 16:55:09 CDT 2006


On Thursday 21 September 2006 18:24, Travis Oliphant wrote:
> Martin Wiechert wrote:
> > Thanks Travis.
> >
> > Do I understand correctly that the only way to be really safe is to make
> > a copy and not to export a reference to it?
> > Because anybody having a reference to the owner of the data can override
> > the flag?
>
> No, that's not quite correct.   Of course in C, anybody can do anything
> they want to the flags.
>
> In Python, only the owner of the object itself can change the writeable
> flag once it is set to False.   So, if you only return a "view" of the
> array (a.view())  then the Python user will not be able to change the
> flags.
>
> Example:
>
> a = array([1,2,3])
> a.flags.writeable = False
>
> b = a.view()
>
> b.flags.writeable = True   # raises an error.
>
> c = a
> c.flags.writeable = True  # can be done because c is a direct alias to a.
>
> Hopefully, that explains the situation a bit better.
>

It does. Thanks Travis.

> -Travis
>
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