更新时间:2023-11-18 20:12:04
您似乎已经解决了您的问题,但是我仍然想回答这个问题.首先是因为我想尝试一下,其次是因为我认为您在内存管理方面遇到了一些问题,我想指出一点.
You seem to have solved your problems, but I would like to answer the question nevertheless. First because I would like to try it out and second because I think you have some problems with memory management and I would like to point it out.
我们将包装以下简单的C接口:
We will wrap the following simple C-interface:
//creator.h
typedef struct {
int mult;
int add;
} Result;
typedef struct {
int size;
Result *arr;
} ResultArray;
ResultArray create(int size, int *input){
//whole file at the end of the answer
}
处理输入数组并返回结构的C数组以及该数组中元素的数量.
which processes the input-array and return a C-array of structs along with the number of elements in this array.
我们的包装pyx文件如下所示:
Our wrapping pyx-file looks then like following:
#result_import.pyx (verion 0)
cdef extern from "creator.h":
ctypedef struct Result:
int mult
int add
ctypedef struct ResultArray:
int size
Result *arr
ResultArray create(int size, int *input)
def create_structs(int[::1] input_vals):
pass
最值得注意的部分:我使用memoryview(int[::1]
)传递我的输入数组,这有两个优点:
The most notable part: I use a memoryview (int[::1]
) to pass my input array and this has two advantages:
numpy
,array
),这比使用numpy数组更灵活[::1]
)输入是连续的numpy
, array
since Python3) which is more flexible as to use a numpy array[::1]
) that the input is continuous在测试脚本中,我使用numpy,但内置数组也可以使用:
In the test-script I use numpy, but one could also go with build-in array:
#test.py
import result_import
import numpy as np
a=np.array([1,2,3],dtype='int32')
result=result_import.create_structs(a)
for i,el in enumerate(result):
print i, ": mult:", el.mult, " add:", el.add
现在什么都没有了,但是一切都设置好了.
Now nothing works yet, but everything is set up.
第一种情况:我们只想拥有普通的python对象,别无所求!一种可能性是:
First scenario: we just wanna have normal python-objects nothing fancy! One possibility would be:
#result_import.pyx (verion 1)
#from cpython cimport array needed for array.array in Python2
from libc.stdlib cimport free
....
class PyResult:
def __init__(self, mult, add):
self.mult=mult
self.add=add
def create_structs(int[::1] input_vals):
cdef ResultArray res=create(len(input_vals), &input_vals[0])
try:
lst=[]
for i in range(res.size):
lst.append(PyResult(res.arr[i].mult, res.arr[i].add))
finally:
free(res.arr)
return lst
我将整个数据转换为python-objects并使用一个简单的列表.很简单,但是有两点值得注意:
I convert the whole data to python-objects and use a simple list. Very simple, but there are two things worth noting:
try...finally
来确保即使抛出异常也会发生这种情况.NULL
是不够的,我必须调用free
-function.try...finally
to make sure it happens even if an exception is thrown.NULL
, I have to call free
-function.现在我们的test.py
可以工作了-很好!
Now our test.py
works - nice!
第二种情况:但是,如果我只需要一些元素并将其全部转换-则效率很低.此外,我将所有元素两次保留在内存中(至少一段时间)-这是幼稚方法的缺点.因此,我想稍后在程序中的某个位置创建PyResult
-objects.
Second scenario: however if I need only some of the elements and convert them all - it is just inefficient. Furthermore, I keep all elements twice in the memory (at least for some time) - this is a downside of the naive approach. So I would like to create PyResult
-objects on demand somewhere later in program.
让我们写一个包装列表:
Let's write a wrapper list:
#result_import.pyx (verion 2)
...
cdef class WrappingList:
cdef int size
cdef Result *arr
def __cinit__(self):
self.size=0
self.arr=NULL
def __dealloc__(self):
free(self.arr)
print "deallocated"#just a check
def __getitem__(self, index):
if index<0 or index>=self.size:
raise IndexError("list index out of range")
return PyResult(self.arr[index].mult, self.arr[index].add)
def create_structs(int[::1] input_vals):
cdef ResultArray res=create(len(input_vals), &input_vals[0])
lst=WrappingList()
lst.size, lst.arr=res.size, res.arr
return lst
因此,类WrappingList
的行为非常类似于列表,保留整个C数组而不进行复制,并且仅在需要时创建PyResult
对象.值得一提的事情:
So the class WrappingList
behaves a lot like a list, keeps the whole C-array without copying and creates PyResult
-objects only when needed. Things worth mentioning:
__dealloc__
在销毁WrapperingList
对象时被调用-这是我们释放C代码给我们的内存的地方.在test.py
的结尾处,我们应该看到已取消分配",否则出现了问题... __getitem__
用于迭代. __dealloc__
is called when the WrapperingList
-object is destroyed - this is the place where we release the memory which was given to us by the C-code. At the end of test.py
we should see "deallocated", otherwise something gone wrong...__getitem__
is used for iteration. 第三种情况::Python代码不仅应读取结果,还应更改结果,以便将更改后的数据传递回C代码.为此,让我们将PyResult
用作代理:
Third scenario: Python code should not only read the results but also change them, so the changed data can be passed back to the C-code. For that let's make PyResult
a proxy:
#result_import.pyx (verion 3, last)
...
cdef class PyResult:
cdef Result *ptr #ptr to my element
def __init__(self):
self.ptr=NULL
@property
def mult(self):
return self.ptr.mult
@mult.setter
def mult(self, value):
self.ptr.mult = value
@property
def add(self):
return self.ptr.add
@add.setter
def add(self, value):
self.ptr.add = value
cdef class WrappingList:
...
def __getitem__(self, index):
if index>=self.size:
raise IndexError("list index out of range")
res=PyResult()
res.ptr=&self.arr[index]
return res
现在,PyResult
对象拥有指向相应元素的指针,并可以直接在C数组中对其进行更改.但是,我要提一些陷阱:
Now, the PyResult
-object holds a pointer to the corresponding element and can change it directly in the C-array. However, there are some pitfalls, I should mention:
PyResult
的生存期不应超过父对象WrappingList
-对象的生存时间.您可以通过在PyResult
-class中添加对parent的引用来解决此问题.add
或mult
)的成本非常高,因为每次必须创建,注册并删除新的Python对象时,它的成本都很高. PyResult
should not live longer than the parent-WrappingList
-object. You can fix it by adding a reference to parent in the PyResult
-class.add
or mult
) is quite costly, because every time a new Python-object must be created, registered and then deleted. 让我们更改测试脚本,以查看正在使用的代理:
Let's change the test-script, to see the proxies in action:
#test.py(second version)
import result_import
import numpy as np
a=np.array([1,2,3],dtype='int32')
result=result_import.create_structs(a)
for i,el in enumerate(result):
print i, ": mult:", el.mult, " add:", el.add
el.mult, el.add=42*i,21*i
# now print changed values:
for i,el in enumerate(result):
print i, ": mult:", el.mult, " add:", el.add
还有很多需要改进的地方,但我想一个答案就足够了:)
There is still a lot to improve, but I guess enough for one answer:)
附件:
草率的creator.h
-需要检查malloc
的结果:
Sloppy creator.h
- one needs to check the result of malloc
:
//creator.h
typedef struct {
int mult;
int add;
} Result;
typedef struct {
int size;
Result *arr;
} ResultArray;
ResultArray create(int size, int *input){
ResultArray res;
res.size=size;
res.arr=(Result *)malloc(size*sizeof(Result));//todo: check !=0
for(int i=0;i<size;i++){
res.arr[i].mult=2*input[i];
res.arr[i].add=2+input[i];
}
return res;
}
setup.py:
from distutils.core import setup, Extension
from Cython.Build import cythonize
setup(ext_modules=cythonize(Extension(
name='result_import',
sources = ["result_import.pyx"]
)))