在 Python 中将数组/列表的子集引用作为参数传递 [英] Passing subset reference of array/list as an argument in Python

问题描述

我对 Python 有点陌生(1 天)，所以也许我的问题很愚蠢.我已经看过这里，但我可以'没有找到我的答案.

I'm kind of new (1 day) to Python so maybe my question is stupid. I've already looked here but I can't find my answer.

我需要以随机大小的随机偏移量修改数组的内容.我有一个 Python API 可以为我无法修改的 USB 设备连接 DDL.有一个这样的功能:

I need to modify the content of an array at a random offset with a random size. I have a Python API to interface a DDL for an USB device which I can't modify. There is a function just like this one :

def read_device(in_array):
    # The DLL accesses the USB device, reads it into in_array of type array('B')
    # in_array can be an int (the function will create an array with the int 
    # size and return it), or can be an array or, can be a tuple (array, int)

在我的代码中，我创建了一个数组，假设为 64 个字节，我想从第 32 个字节开始读取 16 个字节.在 C 中，我会将 &my_64_array[31] 提供给 read_device 函数.在python中，如果给:

In MY code, I create an array of, let's say, 64 bytes and I want to read 16 bytes starting from the 32rd byte. In C, I'd give &my_64_array[31] to the read_device function. In python, if a give :

read_device(my_64_array[31:31+16])

似乎 in_array 是对给定子集副本的引用，因此 my_64_array 没有被修改.

it seems that in_array is a reference to a copy of the given subset, therefore my_64_array is not modified.

我能做什么?我是否必须拆分 my_64_array 并在 ??

What can I do ? Do I have to split my_64_array and recombine it after ??

推荐答案

正如您所说，如果您将切片输入到函数中，它会创建切片的引用副本.

It's precisely as you say, if you input a slice into a function it creates a reference copy of the slice.

稍后添加它的两种可能方法(假设 read_device 返回相关切片):

Two possible methods to add it later (assuming read_device returns the relevant slice):

my_64_array = my_64_array[:32] + read_device(my_64_array[31:31+16]) + my_64_array[31+16:]
# equivalently, but around 33% faster for even small arrays (length 10), 3 times faster for (length 50)...
my_64_array[31:31+16] = read_device(my_64_array[31:31+16])

所以我认为你应该使用后者.

So I think you should be using the latter.

.

如果它是一个可修改的函数(但在这种情况下不是！)你可以改变你的函数参数(一个是整个数组):

If it was a modifiable function (but it's not in this case!) you could be to change your functions arguments (one is the entire array):

def read_device(the_64_array, start=31, end=47):
   # some code
   the_64_array[start:end] = ... #modifies `in_array` in place

并调用 read_device(my_64_array) 或 read(my_64_array, 31, 31+16).

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