Re: [Numpy-discussion] documentation suggestion
Sun, 12 Apr 2009 17:32:31 -0400, Neal Becker wrote: [clip] Done, but can someone check that what I wrote is accurate? I wrote that changes to the ndarray will change the underlying buffer object. But, the buffer protocol allows for read-only buffers. Not sure what ndarray would do if you tried to write in that case. For read-only buffers, the new array will not be writeable: x=abcde z=np.ndarray((5,), buffer=x, dtype='1S') z[0] = 'x' Traceback (most recent call last): File stdin, line 1, in module RuntimeError: array is not writeable However, you can override this, and misusing it potentially leads to nasty things: x=abcde y=abcde z=np.ndarray((5,), buffer=x, dtype='1S') z.flags.writeable = True z[0] = 'x' x 'xbcde' y 'xbcde' hash(x) -1332677140 hash(abcde) -1332677140 Hashing breaks, and the assumed immutability of strings causes nonlocal effects! *** However, for some reason, I don't see your contribution in the change list: http://docs.scipy.org/numpy/changes/ Can you check if the change you made went through? What page did you edit? -- Pauli Virtanen ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] documentation suggestion
Stéfan van der Walt wrote: Hi Neal 2009/4/11 Neal Becker ndbeck...@gmail.com: I found this misleading. It isn't just used to _fill_ the array - it is the Please create an account on docs.scipy.org, then I'll give you priviledges to edit documentation. Thanks! Stéfan Done, but can someone check that what I wrote is accurate? I wrote that changes to the ndarray will change the underlying buffer object. But, the buffer protocol allows for read-only buffers. Not sure what ndarray would do if you tried to write in that case. ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
[Numpy-discussion] documentation suggestion
numpy.ndarray says:
buffer : object exposing buffer interface, optional
Used to fill the array with data.
I found this misleading. It isn't just used to _fill_ the array - it is the
actual storage for the array. If set to an object exporting the buffer
interface, any updates to the ndarray will change the value of this object.
As an example:
from numpy import *
import eos
import mmap
import os
fd = os.open ('test.dat', os.O_RDWR|os.O_CREAT)
size = 128
os.ftruncate (fd, size)
m = mmap.mmap (fd, size, prot=mmap.PROT_READ|mmap.PROT_WRITE,
flags=mmap.MAP_SHARED)
u = ndarray (shape=(size,), dtype=uint8, buffer=m)
u[:] = 24
mmap exports buffer interface (Also not mentioned in the documentation for
mmap!). Updating the value of u (last line above) will change the file on
disk.
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Re: [Numpy-discussion] documentation suggestion
Hi Neal 2009/4/11 Neal Becker ndbeck...@gmail.com: I found this misleading. It isn't just used to _fill_ the array - it is the Please create an account on docs.scipy.org, then I'll give you priviledges to edit documentation. Thanks! Stéfan ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
