In my old post, I have shared how to use pybind11 to accelerate execution of Python code.
In this post, I will introduce how to use STL containers in exported functions.
If we want to use STL containers for pybind11-exported functions, We need to include the pybind11 stl headers:
#include "pybind11/stl.h"Otherwise, we will see the following error messages:
Did you forget to
#include <pybind11/stl.h>? Or <pybind11/complex.h>, <pybind11/functional.h>, <pybind11/chrono.h>, etc. Some automatic conversions are optional and require extra headers to be included when compiling your pybind11 module.
Here is the content of a test cpp file pybind_stl.cc:
#include <iostream>
#include <map>
#include <string>
#include <vector>
#include "pybind11/pybind11.h"
#include "pybind11/stl.h"
namespace py = pybind11;
using std::string;
using std::vector;
using std::map;
int lcs(string s1, string s2) {
int N1 = s1.size();
int N2 = s2.size();
vector<vector<int>> dp(N1 + 1, vector<int>(N2 + 1, 0));
for (int i = 1; i <= N1; i++) {
for (int j = 1; j <= N2; j++) {
if (s1[i - 1] == s2[j - 1]) {
dp[i][j] = dp[i - 1][j - 1] + 1;
} else {
dp[i][j] = std::max(dp[i - 1][j], dp[i][j - 1]);
}
}
}
return dp[N1][N2];
}
int demo(map<int, int> freq){
int max = -1;
for (auto & item: freq){
if (item.second > max){
max = item.second;
}
}
return max;
}
PYBIND11_MODULE(stl_demo, m) {
m.doc() = "LCS calculation"; // optional module docstring
m.def("lcs", &lcs, "lcs cal", py::arg("s1"), py::arg("s2"));
m.def("demo", &demo, "demo", py::arg("freq"));
}To convert the C++ source file to shared object that can be imported by Python, I also created a Makefile to simplify code development. The content of Makefile is:
.PHONY: test clean
CC := g++
FLAGS := -Wall -std=c++11 -shared -fPIC
INC := $(shell python3 -m pybind11 --include)
SUFFIX := $(shell python3-config --extension-suffix)
CC_FILE := pybind_stl.cc
OBJ := stl_demo$(SUFFIX)
$(OBJ): $(CC_FILE)
$(CC) $(FLAGS) $(INC) $< -o $(OBJ)
test: $(OBJ)
python test.py
clean:
rm *.soWe use the following test.py to check if the cpp code works as expected:
from stl_demo import lcs, demo
def main():
s1 = "afb"
s2 = "acfb"
print(f"lcs len: {lcs(s1, s2)}")
freq = {2: 3, 1: 4, 3: 5}
max_cnt = demo(freq)
print(f"max cnt: {max_cnt}")
if __name__ == "__main__":
main()To test the demo code, simply run:
If everything works correctly, we will get the following result:
lcs len: 3
max cnt: 5
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