问题描述
在 Cython 中，创建 int 的 C++ 向量的 Python 扩展类非常容易
# vector_int.pyx
# distutils: language = c++
from libcpp.stack cimport stack
from libcpp.vector cimport vector
cdef class VectorInt:
cdef vector[int] v
def __cinit__(self,count):
self.v = [0] * count # <-- Works! Allocate variable length of zeros
def set(self,idx,x):
self.v[idx] = x
def get(self,idx):
return self.v[idx]
def test_vector_int_stack():
v = VectorInt(11)
v.set(0,42)
assert v.get(0) == 42
但是如何创建int 的堆栈对象向量 的Python 扩展类？
# vector_stack_int.pyx
# distutils: language = c++
from libcpp.stack cimport stack
from libcpp.vector cimport vector
cdef class VectorStackInt:
cdef vector[stack[long]] v
def __cinit__(self,count):
for i in range(count):
self.v.push_back((new stack[long]())) # <--- Error here?!
def set(self,x):
self.v[idx].push(x)
def get(self,idx):
return self.v[idx].top()
这会失败，因为 new 返回一个指向新堆栈的指针，
Error compiling Cython file:
------------------------------------------------------------
...
cdef vector[stack[long]] v
def __cinit__(self,count):
for i in range(count):
self.v.push_back((new stack[long]())) # <--- Error here?!
^
------------------------------------------------------------
pvtracec/libs/simple.pyx:58:45: Cannot assign type 'stack[long] *' to 'stack[long]'
解决方法
糟糕...只需删除 new。
像malloc一样，C++的new分配内存并返回一个指向它的指针。这里想其实是想直接引用对象。
cdef class VectorStackInt:
cdef vector[stack[long]] v
def __cinit__(self,count):
for i in range(count):
self.v.push_back(stack[long]()) # <--- Remove `new`!
def push(self,idx,x):
self.v[idx].push(x)
def pop(self,idx):
self.v[idx].pop()
def top(self,idx):
return self.v[idx].top()
def test_vector_stack_int():
v = VectorStackInt(11)
v.push(0,42)
v.push(0,43)
v.top(0) == 43
v.pop(0)
v.top(0) == 42