{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# ctypes" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 基本用法" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "`ctypes` 是一个方便 `Python` 调用本地已经编译好的外部库的模块。" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": true }, "outputs": [], "source": [ "from ctypes import util, CDLL" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## 标准 C 库" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "使用 `util` 来找到标准 `C` 库：" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "msvcr90.dll\n" ] } ], "source": [ "libc_name = util.find_library('c')\n", "\n", "# on WINDOWS\n", "print libc_name" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "使用 `CDLL` 来加载 `C` 库：" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": true }, "outputs": [], "source": [ "libc = CDLL(libc_name)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "libc 包含 `C` 标准库中的函数：" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "<_FuncPtr object at 0x0000000003CEE048>" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "libc.printf" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "调用这个函数：" ] }, { "cell_type": "code", "execution_count": 5, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "9" ] }, "execution_count": 5, "metadata": {}, "output_type": "execute_result" } ], "source": [ "libc.printf(\"%s, %d\\n\", \"hello\", 5)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "这里显示的 `9` 是 `printf` 的返回值表示显示的字符串的长度（包括结尾的 `'\\0'`），但是并没有显示结果，原因是 `printf` 函数默认是写在标准输出流上的，与 `IPython` 使用的输出流不一样，所以没有显示结果。" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## C 数学库" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "找到数学库：" ] }, { "cell_type": "code", "execution_count": 6, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "msvcr90.dll\n" ] } ], "source": [ "libm_name = util.find_library('m')\n", "\n", "print libm_name" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "调用 `atan2` 函数：" ] }, { "cell_type": "code", "execution_count": 7, "metadata": { "collapsed": false }, "outputs": [ { "ename": "ArgumentError", "evalue": "argument 1: : Don't know how to convert parameter 1", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mArgumentError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m()\u001b[0m\n\u001b[0;32m 1\u001b[0m \u001b[0mlibm\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mCDLL\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mlibm_name\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m 2\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[0mlibm\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0matan2\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m1.0\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;36m2.0\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mArgumentError\u001b[0m: argument 1: : Don't know how to convert parameter 1" ] } ], "source": [ "libm = CDLL(libm_name)\n", "\n", "libm.atan2(1.0, 2.0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "调用这个函数出错，原因是我们需要进行一些额外工作，告诉 `Python` 函数的参数和返回值是什么样的：" ] }, { "cell_type": "code", "execution_count": 8, "metadata": { "collapsed": false }, "outputs": [], "source": [ "from ctypes import c_double\n", "\n", "libm.atan2.argtypes = [c_double, c_double]\n", "libm.atan2.restype = c_double" ] }, { "cell_type": "code", "execution_count": 9, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "0.4636476090008061" ] }, "execution_count": 9, "metadata": {}, "output_type": "execute_result" } ], "source": [ "libm.atan2(1.0, 2.0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "与 `Python` 数学库中的结果一致：" ] }, { "cell_type": "code", "execution_count": 10, "metadata": { "collapsed": true }, "outputs": [], "source": [ "from math import atan2" ] }, { "cell_type": "code", "execution_count": 11, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "0.4636476090008061" ] }, "execution_count": 11, "metadata": {}, "output_type": "execute_result" } ], "source": [ "atan2(1.0, 2.0)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## Numpy 和 ctypes" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "假设我们有这样的一个函数：\n", "```c\n", "float _sum(float *vec, int len) {\n", " float sum = 0.0;\n", " int i;\n", " for (i = 0; i < len; i++) {\n", " sum += vec[i];\n", " }\n", " return sum\n", "}\n", "```\n", "\n", "并且已经编译成动态链接库，那么我们可以这样调用：\n", "\n", "```python\n", "from ctypes import c_float, CDLL, c_int\n", "from numpy import array, float32\n", "from numpy.ctypeslib import ndpointer\n", "\n", "x = array([1,2,3,4], dtype=float32)\n", "\n", "lib = CDLL()\n", "\n", "ptr = ndpointer(float32, ndim=1, flags='C')\n", "lib._sum.argtypes = [ptr, c_int]\n", "lib._sum.restype = c_float\n", "\n", "result = lib._sum(x, len(x))\n", "```" ] } ], "metadata": { "kernelspec": { "display_name": "Python 2", "language": "python", "name": "python2" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 2 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython2", "version": "2.7.10" } }, "nbformat": 4, "nbformat_minor": 0 }