On 2021年10月10日 19:20, Gregory P. Smith wrote:
On Sun, Oct 10, 2021 at 7:25 AM Facundo Batista
<[email protected] <mailto:[email protected]>> wrote:
Hello everyone!
I need to pack a long list of numbers into shared memory, so I thought
about using `struct.pack_into`.
Its signature is
struct.pack_into(format, buffer, offset, v1, v2, ...)
I have a long list of nums (several millions), ended up doing the
following:
struct.pack_into(f'{len(nums)}Q', buf, 0, *nums)
However, passing all nums as `*args` is very inefficient [0]. So I
started wondering why we don't have something like:
struct.pack_into(format, buffer, offset, values=values)
which would receive the list of values directly.
Is that because my particular case is very uncommon? Or maybe we *do*
want this but we don't have it yet? Or do we already have a better way
of doing this?
Thanks!
[0] https://linkode.org/#95ZZtVCIVtBbx72dURK7a4
<https://linkode.org/#95ZZtVCIVtBbx72dURK7a4>
My first reaction on seeing things like this is "Why not use a numpy.array?"
Does what you have really need to be a long list? If so, that's already
a huge amount of Python object storage as it is. Is it possible for your
application to have kept that in a numpy array for the entirety of the
data lifetime?
https://numpy.org/doc/stable/reference/routines.array-creation.html
<https://numpy.org/doc/stable/reference/routines.array-creation.html>
I'm not saying the stdlib shouldn't have a better way to do this by not
abusing *args as an API, just that other libraries solve the larger
problem of data-memory-inefficiency in their own way already.
/(neat tricks from others regarding stdlib array, shm, & memoryview even
if... not ideal)/
Maybe what's needed is to add, say, '*' to the format string to indicate
that multiple values should come from an iterable, e.g.:
struct.pack_into(f'{len(nums)}*Q', buf, 0, nums)
in this case len(nums) from the nums argument.
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