第四章  1 程序控制结构——条件表达式.ipynb

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   "source": [
    "# 4.1 条件表达式"
   ]
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   "source": [
    "### **关系运算符**"
   ]
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     "text": [
      "True\n"
     ]
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   "source": [
    "print(1<3>2)"
   ]
  },
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   "cell_type": "markdown",
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   "source": [
    "- 条件表达式中不允许使用赋值运算符“=”，用“==”代替"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
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     "ename": "SyntaxError",
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     "output_type": "error",
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      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-7-766b569101c6>\"\u001b[1;36m, line \u001b[1;32m2\u001b[0m\n\u001b[1;33m    if a = 3:\u001b[0m\n\u001b[1;37m         ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
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   ],
   "source": [
    "a = 3\n",
    "if a = 3:\n",
    "    print(\"b = 3\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- 关系运算符具有惰性计算的特点，只计算必须计算的值，而不是计算关系表达式中的每个表达式"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
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     "name": "stdout",
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      "False\n"
     ]
    }
   ],
   "source": [
    "print(1>2>xxx)"
   ]
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### **逻辑运算符**"
   ]
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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- and、or、not\n",
    "- 具有短路求值或惰性求值的特点\n",
    "- 0为False，其余为True"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "- 下边函数使用指定的分隔符把多个字符串连接成一个字符串，默认分隔符为逗号"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "1,2,3,4,5\n",
      "1:2:3:4:5\n"
     ]
    }
   ],
   "source": [
    "def Join(chList,sep = None):\n",
    "    return (sep or ',').join(chList)\n",
    "chTest = ['1','2','3','4','5']\n",
    "print(Join(chTest))\n",
    "print(Join(chTest,':'))"
   ]
  }
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