On 03/03/2014 00:07, Juraj Ivančić wrote:
Is it possible to somehow 'steal' bytearray's buffer and make it a
read-only bytes? I failed to find a way to do this, and would like to
make sure.
My use case is, I would expect, fairly common. I read a certain
(potentially very large) amount of data from the network into a
pre-allocated bytearray. From that point on, this data is logically
read-only. To prevent making redundant copies, I wrap it in a
memoryview, and then slice and dice it. The problem with this memoryview
is that it, and its slices, are considered writable, and thus cannot be
hashed:
ValueError: cannot hash writable memoryview object
The only way (AFAICT) to make this work is to first create a bytes
object from bytearray, but this copies the data. I don't need this copy,
so I'd like to avoid it, because of both principle and performance reasons.
Is there any reason why bytearray isn't able to release/convert its
buffer to bytes? I see that it has a clear() method which... well...
clears it. The former would be much more useful.
I would also be content if there is some way of making memoryview
artificially read-only to avoid the above error.
Any help/thoughts/comments are highly appreciated.
If your data is readonly why can't you simply read it as bytes in the
first place? Failing that from
http://docs.python.org/3/library/stdtypes.html#memoryview
tobytes() - Return the data in the buffer as a bytestring. This is
equivalent to calling the bytes constructor on the memoryview.
>>> m = memoryview(b"abc")
>>> m.tobytes()
b'abc'
>>> bytes(m)
b'abc'
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