machinelearning_notebook/0_python/2_Print_Statement.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Print 函数"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`print` 是Python内置的一个函数，可以用下列不同的方式使用。\n",
    "\n",
    "    - print(\"Hello World\")\n",
    "    - print(\"Hello\", <Variable Containing the String>)\n",
    "    - print(\"Hello\" + <Variable Containing the String>)\n",
    "    - print(\"Hello %s\" % <variable containing the string>)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**需要注意的是，Python2中`print`是一个语句，但是在Python3变成函数，打印的内容需要用`()`括起来**"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 1. 打印字符串"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello World\n"
     ]
    }
   ],
   "source": [
    "print(\"Hello World\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "在Python中，**单引号**、**双引号**和**三引号**用于表示字符串。\n",
    "* 大部分情况下单引号用于声明一个字符。\n",
    "* 声明一行时使用双引号，声明段落/多行时使用三引号。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hey\n",
      "line1line2\n"
     ]
    }
   ],
   "source": [
    "print('Hey')\n",
    "a = 'line1\\\n",
    "line2\\\n",
    "\\\n",
    "'\n",
    "print(a)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "My name is Rajath Kumar M.P.\n",
      "\n",
      "I love Python.\n"
     ]
    }
   ],
   "source": [
    "print(\"\"\"My name is Rajath Kumar M.P.\n",
    "\n",
    "I love Python.\"\"\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "字符串可以分配给变量 `string1` 和 `string2`，使用`print`语句时可以调用。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "scrolled": true
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello World\n",
      "Hello World !\n"
     ]
    }
   ],
   "source": [
    "string1 = 'World'\n",
    "print('Hello', string1)\n",
    "\n",
    "string2 = '!'\n",
    "print('Hello', string1, string2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "字符串连接是两个字符串的“加法”。注意，在连接时，字符串之间不会有空格。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "HelloWorld!\n"
     ]
    }
   ],
   "source": [
    "print('Hello' + string1 + string2)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 2. 打印格式化数据"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "`%s` 用于引用包含字符串的变量。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello World\n"
     ]
    }
   ],
   "source": [
    "print(\"Hello %s\" % string1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "相似地，当我们使用其他的数据类型时\n",
    "\n",
    "    - %s -> string\n",
    "    - %d -> Integer\n",
    "    - %f -> Float\n",
    "    - %o -> Octal\n",
    "    - %x -> Hexadecimal\n",
    "    - %e -> exponential\n",
    "   \n",
    "这可以用于`print`函数本身内部的转换。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Actual Number = 18\n",
      "Float of the number = 18.000000\n",
      "Octal equivalent of the number = 22\n",
      "Hexadecimal equivalent of the number = 12\n",
      "Exponential equivalent of the number = 1.800000e+01\n"
     ]
    }
   ],
   "source": [
    "print(\"Actual Number = %d\" % 18)\n",
    "print(\"Float of the number = %f\" % 18)\n",
    "print(\"Octal equivalent of the number = %o\" % 18)\n",
    "print(\"Hexadecimal equivalent of the number = %x\" % 18)\n",
    "print(\"Exponential equivalent of the number = %e\" % 18)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "当引用多个变量时使用圆括号。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello World !\n"
     ]
    }
   ],
   "source": [
    "print(\"Hello %s %s\" % (string1,string2))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 3. 其他例子"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "下面是使用print语句的其他不同方式。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I want to be printed here\n"
     ]
    }
   ],
   "source": [
    "print(\"I want to be printed %s\" % 'here')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "_A_A_A_A_A_A_A_A_A_A\n"
     ]
    }
   ],
   "source": [
    "print('_A'*10)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Jan\n",
      "Feb\n",
      "Mar\n",
      "Apr\n",
      "May\n",
      "Jun\n",
      "Jul\n",
      "Aug\n"
     ]
    }
   ],
   "source": [
    "print(\"Jan\\nFeb\\nMar\\nApr\\nMay\\nJun\\nJul\\nAug\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Jan\n",
      "Feb\n",
      "Mar\n",
      "Apr\n",
      "May\n",
      "Jun\n",
      "Jul\n",
      "Aug\n"
     ]
    }
   ],
   "source": [
    "print(\"\\n\".join(\"Jan Feb Mar Apr May Jun Jul Aug\".split(\" \")))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 17,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I want \\n to be printed.\n"
     ]
    }
   ],
   "source": [
    "print(\"I want \\\\n to be printed.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n",
      "Routine:\n",
      "\t- Eat\n",
      "\t- Sleep\n",
      "\t- Repeat\n",
      "\n"
     ]
    }
   ],
   "source": [
    "print(\"\"\"\n",
    "Routine:\n",
    "\\t- Eat\n",
    "\\t- Sleep\\n\\t- Repeat\n",
    "\"\"\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## 4. `PrecisionWidth`和`FieldWidth`"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Fieldwidth是整个数字的宽度，精度是向右的宽度。你可以根据需要改变这些宽度。\n",
    "\n",
    "默认的精度宽度设置为6。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'3.121312'"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"%f\" % 3.121312312312"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "注意，最多返回6个小数点。要指定小数点的数目，使用'%(fieldwidth).(precisionwidth)f'。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'3.12131'"
      ]
     },
     "execution_count": 20,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"%.5f\" % 3.121312312312"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如果字段宽度设置超过所需，则数据将自己对齐以调整到指定的值。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 21,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'-33.12131'"
      ]
     },
     "execution_count": 21,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"%9.5f\" % -33.121312312312"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "零填充通过在字段宽度的开始处添加一个0来完成。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 22,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'00000000000003.12131'"
      ]
     },
     "execution_count": 22,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"%020.5f\" % 3.121312312312"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "为了正确对齐，字段宽度中的空格可以留空，以便在使用负数时保持正确的对齐。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      " 3.121312\n",
      "-3.121312\n"
     ]
    }
   ],
   "source": [
    "print(\"% 9f\" % 3.121312312312)\n",
    "print(\"% 9f\" % -3.121312312312)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "通过在字段宽度的开始处添加一个+号，可以在正数的开始处返回'+'号。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "+3.121312\n",
      "-3.121312\n"
     ]
    }
   ],
   "source": [
    "print(\"%+9f\" % 3.121312312312)\n",
    "print(\"% 9f\" % -3.121312312312)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "如上所述，当提到的字段宽度大于实际字段宽度时，数据右对齐。但是可以通过在字段宽度中指定一个负符号来实现左对齐。"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'3.121    '"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "\"%-9.3f\" % 3.121312312312"
   ]
  }
 ],
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