02-python-essentials/02.18-modules-and-packages.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 模块和包"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 模块"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python会将所有 `.py` 结尾的文件认定为Python代码文件，考虑下面的脚本 `ex1.py` ："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwriting ex1.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile ex1.py\n",
    "\n",
    "PI = 3.1416\n",
    "\n",
    "def sum(lst):\n",
    "    tot = lst[0]\n",
    "    for value in lst[1:]:\n",
    "        tot = tot + value\n",
    "    return tot\n",
    "    \n",
    "w = [0, 1, 2, 3]\n",
    "print sum(w), PI"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以执行它："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6 3.1416\n"
     ]
    }
   ],
   "source": [
    "%run ex1.py"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "这个脚本可以当作一个模块，可以使用`import`关键词加载并执行它（这里要求`ex1.py`在当前工作目录）："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6 3.1416\n"
     ]
    }
   ],
   "source": [
    "import ex1"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<module 'ex1' from 'ex1.py'>"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ex1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在导入时，**Python**会执行一遍模块中的所有内容。\n",
    "\n",
    "`ex1.py` 中所有的变量都被载入了当前环境中，不过要使用\n",
    "\n",
    "    ex1.变量名\n",
    "\n",
    "的方法来查看或者修改这些变量："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3.1416\n"
     ]
    }
   ],
   "source": [
    "print ex1.PI"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "3.141592653\n"
     ]
    }
   ],
   "source": [
    "ex1.PI = 3.141592653\n",
    "print ex1.PI"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "还可以用\n",
    "\n",
    "    ex1.函数名\n",
    "\n",
    "调用模块里面的函数："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "9\n"
     ]
    }
   ],
   "source": [
    "print ex1.sum([2, 3, 4])"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "为了提高效率，**Python**只会载入模块一次，已经载入的模块再次载入时，Python并不会真正执行载入操作，哪怕模块的内容已经改变。\n",
    "\n",
    "例如，这里重新导入 `ex1` 时，并不会执行 `ex1.py` 中的 `print` 语句："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "import ex1"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "需要重新导入模块时，可以使用`reload`强制重新载入它，例如："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "6 3.1416\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "<module 'ex1' from 'ex1.pyc'>"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "reload(ex1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "删除之前生成的文件："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import os\n",
    "os.remove('ex1.py')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## `__name__` 属性"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "有时候我们想将一个 `.py` 文件既当作脚本，又能当作模块用，这个时候可以使用 `__name__` 这个属性。\n",
    "\n",
    "只有当文件被当作脚本执行的时候， `__name__`的值才会是 `'__main__'`，所以我们可以："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Writing ex2.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile ex2.py\n",
    "\n",
    "PI = 3.1416\n",
    "\n",
    "def sum(lst):\n",
    "    \"\"\" Sum the values in a list\n",
    "    \"\"\"\n",
    "    tot = 0\n",
    "    for value in lst:\n",
    "        tot = tot + value\n",
    "    return tot\n",
    "\n",
    "def add(x, y):\n",
    "    \" Add two values.\"\n",
    "    a = x + y\n",
    "    return a\n",
    "\n",
    "def test():\n",
    "    w = [0,1,2,3]\n",
    "    assert(sum(w) == 6)\n",
    "    print 'test passed.'\n",
    "    \n",
    "if __name__ == '__main__':\n",
    "    test()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "运行文件："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "test passed.\n"
     ]
    }
   ],
   "source": [
    "%run ex2.py"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "当作模块导入， `test()` 不会执行："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import ex2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "但是可以使用其中的变量："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3.1416"
      ]
     },
     "execution_count": 14,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ex2.PI"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "使用别名："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "3.1416"
      ]
     },
     "execution_count": 15,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import ex2 as e2\n",
    "e2.PI"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 其他导入方法"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "可以从模块中导入变量："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "from ex2 import add, PI"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "使用 `from` 后，可以直接使用 `add` ， `PI`："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "5"
      ]
     },
     "execution_count": 17,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "add(2, 3)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "或者使用 `*` 导入所有变量："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "data": {
      "text/plain": [
       "7.5"
      ]
     },
     "execution_count": 18,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "from ex2 import *\n",
    "add(3, 4.5)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "这种导入方法不是很提倡，因为如果你不确定导入的都有哪些，可能覆盖一些已有的函数。\n",
    "\n",
    "删除文件："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "import os\n",
    "os.remove('ex2.py')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 包"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "假设我们有这样的一个文件夹：\n",
    "\n",
    "foo/\n",
    "- `__init__.py` \n",
    "- `bar.py` (defines func)\n",
    "- `baz.py` (defines zap)\n",
    "\n",
    "这意味着 foo 是一个包，我们可以这样导入其中的内容：\n",
    "\n",
    "```python    \n",
    "from foo.bar import func\n",
    "from foo.baz import zap\n",
    "```\n",
    "\n",
    "`bar` 和 `baz` 都是 `foo` 文件夹下的 `.py` 文件。\n",
    "\n",
    "导入包要求：\n",
    "- 文件夹 `foo` 在**Python**的搜索路径中\n",
    "- `__init__.py` 表示 `foo` 是一个包，它可以是个空文件。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "## 常用的标准库"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- re 正则表达式\n",
    "- copy 复制\n",
    "- math, cmath 数学\n",
    "- decimal, fraction\n",
    "- sqlite3 数据库\n",
    "- os, os.path 文件系统\n",
    "- gzip, bz2, zipfile, tarfile 压缩文件\n",
    "- csv, netrc 各种文件格式\n",
    "- xml\n",
    "- htmllib\n",
    "- ftplib, socket\n",
    "- cmd 命令行\n",
    "- pdb \n",
    "- profile, cProfile, timeit\n",
    "- collections, heapq, bisect 数据结构\n",
    "- mmap\n",
    "- threading, Queue 并行\n",
    "- multiprocessing\n",
    "- subprocess\n",
    "- pickle, cPickle\n",
    "- struct"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {
    "collapsed": true
   },
   "source": [
    "## PYTHONPATH设置"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Python的搜索路径可以通过环境变量PYTHONPATH设置，环境变量的设置方法依操作系统的不同而不同，具体方法可以网上搜索。"
   ]
  }
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