{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Keyboard input to Python\n",
    "\n",
    "Python programs can read input from the keyboard. They do this with the function `input()`, as is shown in the following example."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "What's your name? Tim\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nice to meet you Tim!\n"
     ]
    },
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "How old are you? 137\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "So, you are already 137 years old Tim!\n"
     ]
    }
   ],
   "source": [
    "name = input(\"What's your name?\")\n",
    "print(\"Nice to meet you \" + name + \"!\")\n",
    "age = input(\"How old are you?\")\n",
    "print(\"So, you are already\",age,\"years old\",name,\"\\b!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can check the type of the input as below:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Type of name is <class 'str'>\n",
      "Type of age is <class 'str'>\n"
     ]
    }
   ],
   "source": [
    "print(\"Type of name is\",type(name))\n",
    "print(\"Type of age is\",type(age))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Everything (whether numbers or letters) is read as strings. This means the following code will not work (try it!):"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "What's your name? Tim\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nice to meet you Tim!\n"
     ]
    },
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "How old are you? 137\n"
     ]
    },
    {
     "ename": "TypeError",
     "evalue": "unsupported operand type(s) for -: 'int' and 'str'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-3-97554a4d31b9>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      5\u001b[0m \u001b[0mage\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0minput\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"How old are you?\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      6\u001b[0m \u001b[1;31m#\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 7\u001b[1;33m \u001b[0mretireIn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mretirementAge\u001b[0m \u001b[1;33m-\u001b[0m \u001b[0mage\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      8\u001b[0m \u001b[1;32mif\u001b[0m \u001b[0mretireIn\u001b[0m \u001b[1;33m>\u001b[0m \u001b[1;36m0\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      9\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"I guess you will retire in\"\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mretireIn\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;34m\"years,\"\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mname\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;34m\"\\b.\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mTypeError\u001b[0m: unsupported operand type(s) for -: 'int' and 'str'"
     ]
    }
   ],
   "source": [
    "retirementAge = 67\n",
    "#\n",
    "name = input(\"What's your name?\")\n",
    "print(\"Nice to meet you \" + name + \"!\")\n",
    "age = input(\"How old are you?\")\n",
    "#\n",
    "retireIn = retirementAge - age\n",
    "if retireIn > 0:\n",
    "    print(\"I guess you will retire in\",retireIn,\"years,\",name,\"\\b.\")\n",
    "else:\n",
    "    print(\"I guess you retired\",-retireIn,\"years ago,\",name,\"\\b.\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Changing the relevant string's type to `int` or `float` as appropriate fixes the problem."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "What's your name? Tim\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nice to meet you Tim!\n"
     ]
    },
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "How old are you? 137\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I guess you retired 70 years ago, Tim.\n"
     ]
    }
   ],
   "source": [
    "name = input(\"What's your name?\")\n",
    "print(\"Nice to meet you \" + name + \"!\")\n",
    "age = input(\"How old are you?\")\n",
    "#\n",
    "retireIn = retirementAge - int(age)\n",
    "if retireIn > 0:\n",
    "    print(\"I guess you will retire in\",retireIn,\"years,\",name,\"\\b.\")\n",
    "else:\n",
    "    print(\"I guess you retired\",-retireIn,\"years ago,\",name,\"\\b.\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Usually a good idea to check that inputs are sensible. Here we check that the age entered is in the range 0 < age < 120 years. If the age is out of range, we ask that it be re-entered. If an out-of-range answer is given more than 3 times in a row, print an error message and stop the program!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "What's your name? Tim\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nice to meet you Tim!\n"
     ]
    },
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "How old are you? 137\n",
      "How old are you? 136\n",
      "How old are you? 135\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Too many incorrect inputs!\n"
     ]
    },
    {
     "ename": "SystemExit",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "An exception has occurred, use %tb to see the full traceback.\n",
      "\u001b[1;31mSystemExit\u001b[0m\n"
     ]
    },
    {
     "name": "stderr",
     "output_type": "stream",
     "text": [
      "C:\\Users\\green\\Anaconda3\\lib\\site-packages\\IPython\\core\\interactiveshell.py:3327: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.\n",
      "  warn(\"To exit: use 'exit', 'quit', or Ctrl-D.\", stacklevel=1)\n"
     ]
    }
   ],
   "source": [
    "import sys\n",
    "#\n",
    "# Alternative one\n",
    "name = input(\"What's your name?\")\n",
    "print(\"Nice to meet you \" + name + \"!\")\n",
    "#\n",
    "count = 0\n",
    "maxCount = 3\n",
    "while count < maxCount:\n",
    "    age = input(\"How old are you?\")\n",
    "    if int(age) > 0 and int(age) < 120:\n",
    "        break\n",
    "    count += 1\n",
    "else:\n",
    "    print(\"Too many incorrect inputs!\")\n",
    "    sys.exit()\n",
    "#\n",
    "retireIn = retirementAge - int(age)\n",
    "if retireIn > 0:\n",
    "    print(\"I guess you will retire in\",retireIn,\"years,\",name,\"\\b.\")\n",
    "else:\n",
    "    print(\"I guess you retired\",-retireIn,\"years ago,\",name,\"\\b.\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "ename": "SystemExit",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mSystemExit\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-5-e6c6f04c5b0f>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m     14\u001b[0m \u001b[1;32melse\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     15\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Too many incorrect inputs!\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 16\u001b[1;33m     \u001b[0msys\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mexit\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     17\u001b[0m \u001b[1;31m#\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     18\u001b[0m \u001b[0mretireIn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mretirementAge\u001b[0m \u001b[1;33m-\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mage\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mSystemExit\u001b[0m: "
     ]
    }
   ],
   "source": [
    "# The following command will give the last full traceback, only relevant if it was caused by an error at this point!\n",
    "%tb"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "What's your name? Tim\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Nice to meet you Tim!\n"
     ]
    },
    {
     "name": "stdin",
     "output_type": "stream",
     "text": [
      "How old are you? 45\n"
     ]
    },
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I guess you will retire in 22 years, Tim.\n"
     ]
    }
   ],
   "source": [
    "import sys\n",
    "#\n",
    "# Alternative two\n",
    "name = input(\"What's your name?\")\n",
    "print(\"Nice to meet you \" + name + \"!\")\n",
    "#\n",
    "for count in range(0, maxCount):\n",
    "    age = input(\"How old are you?\")\n",
    "    if int(age) > 0 and int(age) < 120:\n",
    "        break\n",
    "#\n",
    "if count < maxCount - 1:\n",
    "    retireIn = retirementAge - int(age)\n",
    "    if retireIn > 0:\n",
    "        print(\"I guess you will retire in\",retireIn,\"years,\",name,\"\\b.\")\n",
    "    else:\n",
    "        print(\"I guess you retired\",-retireIn,\"years ago,\",name,\"\\b.\")\n",
    "else:\n",
    "    print(\"Too many incorrect inputs!\")\n",
    "    sys.exit()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "ename": "SystemExit",
     "evalue": "",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mSystemExit\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-5-e6c6f04c5b0f>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m     14\u001b[0m \u001b[1;32melse\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     15\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"Too many incorrect inputs!\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 16\u001b[1;33m     \u001b[0msys\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mexit\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     17\u001b[0m \u001b[1;31m#\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     18\u001b[0m \u001b[0mretireIn\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mretirementAge\u001b[0m \u001b[1;33m-\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mage\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mSystemExit\u001b[0m: "
     ]
    }
   ],
   "source": [
    "%tb"
   ]
  }
 ],
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