Using_Python_to_Interact_with_the_Operating_System/module4.ipynb

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  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Reading data interactively"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "cat hello.py\n",
    "#!/usr/bin/env python3\n",
    "\n",
    "name = input(\"Please enter your name: \")\n",
    "print(\"Hello, \" + name)\n",
    "\n",
    "# ./hello.py \n",
    "# Please enter your name: Roger\n",
    "# #Output will be Hello, Roger"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# defining a function called 'to_seconds' which takes hours, minutes and seconds as\n",
    "# inputs and returns their total equivalent in seconds by multiplying each with its\n",
    "# corresponding factor (3600 for hours, 60 for minutes) and then summing them up.\n",
    "def to_seconds(hours, minutes, seconds):\n",
    "    return hours*3600+minutes*60+seconds\n",
    "\n",
    "# Print a welcome message to the user\n",
    "print(\"Welcome to this time converter\")\n",
    "\n",
    "# set 'cont' variable to \"y\" initially for entering into while loop.\n",
    "cont = \"y\"\n",
    "\n",
    "# while condition is true (user wants to continue), keep asking the\n",
    "# number of hours, minutes and seconds from the user and print their total equivalent\n",
    "# in seconds by calling 'to_seconds' function. Ask if they want to do another conversion.\n",
    "# If not, break the loop.\n",
    "while(cont.lower() == \"y\"):\n",
    "    hours = int(input(\"Enter the number of hours: \"))\n",
    "    minutes = int(input(\"Enter the number of minutes: \"))\n",
    "    seconds = int(input(\"Enter the number of seconds: \"))\n",
    "\n",
    "    print(\"That's {} seconds\".format(to_seconds(hours, minutes, seconds)))\n",
    "    print()\n",
    "    cont = input(\"Do you want to do another conversion? [y to continue] \")\n",
    "    \n",
    "# print a goodbye message when user decides to stop the program.\n",
    "print(\"Goodbye!\")\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Standard streams\n",
    "I/O Streams"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "cat streams.py\n",
    "#!/usr/bin/env python3\n",
    "\n",
    "data = input(\"This will come from STDIN: \")\n",
    "print(\"Now we write it to STDOUT: \" + data)\n",
    "print(\"Now we generate an error to STDERR: \" + data + 1)\n",
    "\n",
    "./streams.py \n",
    "This will come from STDIN: Python Rocks!\n",
    "Now we write it to STDOUT: Python Rocks!\n",
    "\n",
    "cat greeting.txt \n",
    "Well hello there, STDOUT\n",
    "\n",
    "cat greeting.txt \n",
    "Well hello there, STDOUT\n",
    "\n",
    "ls -z"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Environment variables"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "HOME: /config\n",
      "SHELL: \n",
      "FRUIT: \n"
     ]
    }
   ],
   "source": [
    "# echo $PATH\n",
    "# /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin\n",
    "# cat variables.py\n",
    "#!/usr/bin/env python3\n",
    "import os\n",
    "print(\"HOME: \" + os.environ.get(\"HOME\", \"\"))\n",
    "print(\"SHELL: \" + os.environ.get(\"SHELL\", \"\"))\n",
    "print(\"FRUIT: \" + os.environ.get(\"FRUIT\", \"\"))\n",
    "# ./variables.py\n",
    "# export FRUIT=Pineapple\n",
    "# ./variables.py"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Command-Line Arguments and Exit Status"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "cat parameters.py \n",
    "#!/usr/bin/env python3\n",
    "import sys\n",
    "print(sys.argv)\n",
    "\n",
    "./parameters.py\n",
    "['./parameters.py'] \n",
    "\n",
    "./parameters.py one two three\n",
    "['./parameters.py', 'one', 'two', 'three']\n",
    "…cat example \n",
    "New file created\n",
    "./create_file.py example\n",
    "Error, the file example already exists!\n",
    "echo $?\n",
    "1"
   ]
  }
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