python3.ipynb

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   "source": [
    "# 一、条件语句\n",
    "\n",
    "Python 条件语句跟其他语言基本一致的，都是通过一条或多条语句的执行结果（ True 或者 False ）来决定执行的代码块。\n",
    "\n",
    "Python 程序语言指定任何非 0 和非空（null）值为 True，0 或者 null为 False。\n",
    "\n",
    "执行的流程图如下：\n",
    "\n",
    "![if语句流程图](http://upload-images.jianshu.io/upload_images/2136918-4ee2486190450a1a?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)\n",
    "\n",
    "## 1、if 语句的基本形式 \n",
    "\n",
    "Python 中，if 语句的基本形式如下：\n",
    "\n",
    "``` python\n",
    "if 判断条件：\n",
    "    执行语句……\n",
    "else：\n",
    "    执行语句……\n",
    "```\n",
    "\n",
    "前面也提到过，Python 语言有着严格的缩进要求，因此这里也需要注意缩进，也不要少写了冒号 `:` 。\n",
    "\n",
    "if 语句的判断条件可以用>（大于）、<(小于)、==（等于）、>=（大于等于）、<=（小于等于）来表示其关系。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "results = 59"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "不及格\n"
     ]
    }
   ],
   "source": [
    "if results >= 60:\n",
    "    print('几个')\n",
    "else:\n",
    "    print('不及格')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2、if 语句多个判断条件的形式 \n",
    "\n",
    "有些时候，我们的判断语句不可能只有两个，有些时候需要多个，比如上面的例子中大于 60 的为及格，那我们还要判断大于 90 的为优秀，在 80 到 90 之间的良好呢？\n",
    "\n",
    "这时候需要用到 if 语句多个判断条件，\n",
    "\n",
    "用伪代码来表示：\n",
    "\n",
    "``` python\n",
    "if 判断条件1:\n",
    "    执行语句1……\n",
    "elif 判断条件2:\n",
    "    执行语句2……\n",
    "elif 判断条件3:\n",
    "    执行语句3……\n",
    "else:\n",
    "    执行语句4……\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "良好\n"
     ]
    }
   ],
   "source": [
    "results = 89\n",
    "\n",
    "if results > 90:\n",
    "    print('优秀')\n",
    "elif results > 80:\n",
    "    print('良好')\n",
    "elif results > 60:\n",
    "    print ('及格')\n",
    "else :\n",
    "    print ('不及格')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 3、if 语句多个条件同时判断\n",
    "\n",
    "Python 不像 Java 有 switch 语句，所以多个条件判断，只能用 elif 来实现，但是有时候需要多个条件需同时判断时，可以使用 or （或），表示两个条件有一个成立时判断条件成功；使用 and （与）时，表示只有两个条件同时成立的情况下，判断条件才成功。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "不优秀\n",
      "良好\n"
     ]
    }
   ],
   "source": [
    "java = 86\n",
    "python = 68\n",
    "\n",
    "if java > 80 and  python > 80:\n",
    "    print('优秀')\n",
    "else :\n",
    "    print('不优秀')\n",
    "\n",
    "if ( java >= 80  and java < 90 )  or ( python >= 80 and python < 90):\n",
    "    print('良好')"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "注意：if 有多个条件时可使用括号来区分判断的先后顺序，括号中的判断优先执行，此外 and 和 or 的优先级低于 >（大于）、<（小于）等判断符号，即大于和小于在没有括号的情况下会比与或要优先判断。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# 二、循环语句\n",
    "Python的循环有两种，一种是for...in循环，依次把list或tuple中的每个元素迭代出来，看例子："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Michael\n",
      "Bob\n",
      "Tracy\n"
     ]
    }
   ],
   "source": [
    "names = ['Michael', 'Bob', 'Tracy']  \n",
    "for name in names:          #执行这段代码，会依次打印names的每一个元素\n",
    "    print(name)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "所以for x in ...循环就是把每个元素代入变量x，然后执行缩进块的语句。\n",
    "\n",
    "再比如我们想计算1-10的整数之和，可以用一个sum变量做累加："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "55\n"
     ]
    }
   ],
   "source": [
    "sum = 0\n",
    "for x in [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]:\n",
    "    sum = sum + x\n",
    "print(sum)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如果要计算1-100的整数之和，从1写到100有点困难，幸好Python提供一个range()函数，可以生成一个整数序列，再通过list()函数可以转换为list。比如range(5)生成的序列是从0开始小于5的整数："
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "5050\n"
     ]
    }
   ],
   "source": [
    "sum = 0\n",
    "for x in range(101):\n",
    "    sum = sum + x\n",
    "print(sum)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## while\n",
    "第二种循环是while循环，只要条件满足，就不断循环，条件不满足时退出循环。比如我们要计算100以内所有奇数之和，可以用while循环实现：\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "2500\n"
     ]
    }
   ],
   "source": [
    "sum = 0\n",
    "n = 99\n",
    "while n > 0:\n",
    "    sum = sum + n\n",
    "    n = n - 2\n",
    "print(sum)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在循环内部变量n不断自减，直到变为-1时，不再满足while条件，循环退出。"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## break、continue\n",
    "在循环中，break、continue语句作用跟Java类似"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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