[Python] Passing Numeric Arrays to Python via ctypes Without Prior Knowledge of Array Length

I would like a C++ function return a numeric array (uint8_t* converted from a vector) into a python bytes object. I don't know the length of this array ahead of time. This is numeric data, not a C string that would naturally have a null terminator. I'm having trouble finding any documentation on how to handle the length of the returned C pointer. Presumably, I can't just cast it to bytes since there's no length information in the bytes constructor. I'd like to avoid a really slow for loop.

C++:

uint8_t* cfunc(uint32_t* length_of_return_value); // returns an arbitrary-length numeric vector


Python:

import ctypes as c
c.cdll.LoadLibrary("file.so")
clib = c.CDLL("file.so")
clib.cfunc.argtypes = [c.POINTER(c.c_uint32)]
clib.cfunc.restype = c.POINTER(c.c_uint8)
length_of_return_value = c.c_uint32(0)
x = clib.cfunc(length_of_return_value)
# now what?
assert type(x) in {bytes, list}, "I need this to be a type that's convertible to numpy array"

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