Question

Let’s say I have a 10 element array:

from ctypes import *
arr = c_float * 10

, and I’d like to shrink it to 5 elements. I tried doing something like this:

resize(arr, sizeof(c_float) * 5)
arr = (c_float * 5).from_address(addressof(arr))

But I get a ValueError: minimum size is XXX exception meaning that I can’t shrink the memory, only grow it. If I really want, is it possible to overcome this limitation with a clever hack?

Answer 1

This seems to work just fine:

>>> float_10 = c_float * 10
>>> float_5 = c_float * 5
>>> a1 = float_10(range(10))
>>> a2 = float_5.from_address(addressof(a1))
>>> print list(a1)
[0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0]
>>> print list(a2)
[0.0, 1.0, 2.0, 3.0, 4.0]

EDIT: This doesn’t actually resize the original list though, and addressof(a1) will equal addressof(a2), so the unused bits of the list linger in memory…