Init example with ctypes and pybind11 and cpython

Author: Ailing Zhang

.gitignore

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+build/*
+__pycache__/*
+*.so
+*.egg-info

.gitmodules

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+

CMakeLists.txt

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+cmake_minimum_required(VERSION 3.4...3.18)
+project(sum)
+
+# The following has been moved to setup.py
+# To enable this you'll need a pybind11 submodule
+#add_subdirectory(pybind11)
+#pybind11_add_module(sum_from_pybind11 src/sum_pybind11.cpp)
+#target_include_directories(sum_from_pybind11 PRIVATE src/)
+#target_compile_definitions(sum_from_pybind11 PRIVATE VERSION_INFO=0.1)
+add_library(sum_from_ctypes MODULE src/sum.c)
+

README.md

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+# Compile for ctypes demo
+I didn't bother writing a proper `build_ext` for this so manual copy is required.
+
+```
+mkdir build
+cd build
+cmake .. && make
+cp *.so ../
+```
+
+# Compile pybind11 & cpython demo
+```
+python setup.py build && pip install -e .
+```
+
+# Run
+
+```
+python main.py
+```
+
+# References
+- https://en.wikibooks.org/wiki/Python_Programming/Extending_with_C
+- https://github.com/pybind/python_example
+- https://pgi-jcns.fz-juelich.de/portal/pages/using-c-from-python.html
+- https://gist.github.com/physacco/2e1b52415f3a964ad2a542a99bebed8f
+- https://scipy-lectures.org/advanced/interfacing_with_c/interfacing_with_c.html#id1
+- https://stackoverflow.com/questions/22458298/extending-python-with-c-pass-a-list-to-pyarg-parsetuple

main.py

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+import sum_from_ctypes
+import sum_from_pybind11
+import sum_from_cpython
+import time
+
+N = 50
+
+def timed_run(func, name):
+    a = [1] * 100
+    start = time.time()
+    for _ in range(N):
+        func(a)
+    print(f'{name} took {(time.time() - start) / N}s')
+
+
+timed_run(sum_from_ctypes.my_sum, 'ctypes')
+timed_run(sum_from_pybind11.my_sum, 'pybind')
+timed_run(sum_from_cpython.my_sum, 'cpython')
+

setup.py

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+# DO NOT reorder these imports due to monkey-patch
+from pybind11.setup_helpers import Pybind11Extension
+from distutils.core import setup, Extension
+
+cpython_mod = Extension('sum_from_cpython', sources = ['src/sum_cpython.c'])
+pybind_mod = Pybind11Extension('sum_from_pybind11', sources = ['src/sum_pybind11.cpp'])
+
+setup (name = 'demo',
+        version = '0.0',
+        description = 'This is a demo package',
+        ext_modules = [cpython_mod, pybind_mod])

src/sum.c

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+#include "sum.h"

src/sum.h

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+#include <stdio.h>
+#include <time.h>
+#include <sys/time.h>
+
+int my_sum(int num_numbers, int *numbers) {
+#if 0
+  long start, end;
+  struct timeval timecheck;
+  gettimeofday(&timecheck, NULL);
+  start = (long)timecheck.tv_sec * 1000 * 1000 + (long)timecheck.tv_usec;
+#endif
+  int i;
+  int sum = 0;
+  for (i = 0; i < num_numbers; i++) {
+    sum += numbers[i];
+  }
+#if 0
+  gettimeofday(&timecheck, NULL);
+  end = (long)timecheck.tv_sec * 1000 * 1000 + (long)timecheck.tv_usec;
+  printf("%ld us elapsed\n", (end - start));
+#endif
+  return sum;
+}

src/sum_cpython.c

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+#include <stdio.h>
+#include <Python.h>
+
+// Module method definitions
+static PyObject* my_sum_from_cpython(PyObject *self, PyObject *args) {
+    PyObject *pList;
+    PyObject *pItem;
+    Py_ssize_t n;
+    int i;
+    if (!PyArg_ParseTuple(args, "O!", &PyList_Type, &pList)) {
+      PyErr_SetString(PyExc_TypeError, "parameter must be a list");
+      return NULL;
+    }
+    n = PyList_Size(pList);
+    long sum = 0;
+    for (i = 0; i < n; i++) {
+        pItem = PyList_GetItem(pList, i);
+        if (!PyLong_Check(pItem)) {
+          return NULL;
+        }
+        sum += PyLong_AsLong(pItem);
+    }
+    return Py_BuildValue("l", sum);
+}
+// Method definition object for this extension, these argumens mean:
+// ml_name: The name of the method
+// ml_meth: Function pointer to the method implementation
+// ml_flags: Flags indicating special features of this method, such as
+//          accepting arguments, accepting keyword arguments, being a
+//          class method, or being a static method of a class.
+// ml_doc:  Contents of this method's docstring
+static PyMethodDef sum_from_cpython_methods[] = {
+    {
+        "my_sum", my_sum_from_cpython, METH_VARARGS, ""
+    },
+    {NULL, NULL, 0, NULL}
+};
+
+// Module definition
+// The arguments of this structure tell Python what to call your extension,
+// what it's methods are and where to look for it's method definitions
+static struct PyModuleDef sum_from_cpython_definition = {
+    PyModuleDef_HEAD_INIT,
+    "sum_from_cpython",
+    "A Python module that prints 'sum_from_cpython world' from C code.",
+    -1,
+    sum_from_cpython_methods
+};
+
+// Module initialization
+// Python calls this function when importing your extension. It is important
+// that this function is named PyInit_[[your_module_name]] exactly, and matches
+// the name keyword argument in setup.py's setup() call.
+PyMODINIT_FUNC PyInit_sum_from_cpython(void) {
+    Py_Initialize();
+    return PyModule_Create(&sum_from_cpython_definition);
+}

src/sum_pybind11.cpp

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+#include <pybind11/pybind11.h>
+#include <pybind11/stl.h>
+
+#include "sum.h"
+
+namespace py = pybind11;
+
+PYBIND11_MODULE(sum_from_pybind11, m) {
+  m.def("my_sum", [](std::vector<int>& data) {
+         int sum = my_sum(data.size(), data.data());
+         return sum;
+        }, "");
+}