如何将双指针ctype转换为numpy数组? [英] How can i cast a double pointer ctype to numpy array?

问题描述

嘿，我得到了这段代码，我正在将numpy 2d数组转换为ctype双指针.

Hey I got this code which i'm using to cast numpy 2d array to ctype double pointer.

import ctypes as ct
import numpy as np

arr = np.empty([500, 500], dtype=np.uint8)

UI8Ptr = ct.POINTER(ct.c_uint8)
UI8PtrPtr = ct.POINTER(UI8Ptr)

ct_arr = np.ctypeslib.as_ctypes(arr)
UI8PtrArr = UI8Ptr * ct_arr._length_
ct_ptr = ct.cast(UI8PtrArr(*(ct.cast(row, UI8Ptr) for row in ct_arr)), UI8PtrPtr)

如何将ct_ptr转换回numpy 2d数组?

How can i cast ct_ptr back to numpy 2d array?

推荐答案

注意:这是对一种方法将经历以下状态:

One way would be going through the following states:

1. CTypes 指针
2. Python 列表
3. NumPy 数组

1. CTypes pointer
2. Python lists
3. NumPy array

2个观察结果自动出现:

2 observations automatically arise:

• 这是非常低效的，但是不幸的是，我不知道如何摆脱 #2. (罪魁祸首)
• 指针保存有关基本类型的信息，但不包含有关从其创建数组的维的信息，因此您必须保存"它们，因为在解构"指针时将需要它们

code00.py :

#!/usr/bin/env python3

import sys
import ctypes as ct
import numpy as np


def main():
    dim0 = 3
    dim1 = 4
    arr0 = np.empty([dim0, dim1], dtype=np.uint8)
    print("Initial array:\n{0:}".format(arr0))

    UI8Ptr = ct.POINTER(ct.c_uint8)
    UI8PtrPtr = ct.POINTER(UI8Ptr)

    ct_arr = np.ctypeslib.as_ctypes(arr0)
    UI8PtrArr = UI8Ptr * ct_arr._length_
    ct_ptr = ct.cast(UI8PtrArr(*(ct.cast(row, UI8Ptr) for row in ct_arr)), UI8PtrPtr)

    arr1 = np.array([[ct_ptr[i][j] for j in range(dim1)] for i in range(dim0)], dtype=ct_ptr._type_._type_._type_)
    print("\nFinal array:\n{0:}".format(arr1))
    print("\nEqual arrays: {0:}".format(np.array_equal(arr0, arr1)))


if __name__ == "__main__":
    print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
    main()
    print("\nDone.")

输出:

[cfati@CFATI-5510-0:e:\Work\Dev\StackOverflow\q058781199]> "e:\Work\Dev\VEnvs\py_064_03.07.03_test0\Scripts\python.exe" code00.py
Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] 64bit on win32

Initial array:
[[ 96 100 101 115]
 [105 114 101 100]
 [ 96  96  32 115]]

Final array:
[[ 96 100 101 115]
 [105 114 101 100]
 [ 96  96  32 115]]

Equal arrays: True

Done.

有关此主题的更多信息，请检查

Fore more info on this topic check [SO]: Numpy error when converting array of ctypes types to void pointer (@CristiFati's answer).

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