06 - File Processing/File Processing.ipynb

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   "source": [
    "# File Processing\n",
    "Python has several functions for creating, reading, updating, and deleting files."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### File Opening\n",
    "\n",
    "The <b>open()</b> function takes two parameters; filename, and mode.\n",
    "\n",
    "There are four different methods (modes) for opening a file:\n",
    "```\n",
    "\"r\" - Read - Default value. Opens a file for reading, error if the file does not exist\n",
    "\n",
    "\"a\" - Append - Opens a file for appending, creates the file if it does not exist\n",
    "\n",
    "\"w\" - Write - Opens a file for writing, creates the file if it does not exist\n",
    "\n",
    "\"x\" - Create - Creates the specified file, returns an error if the file exists\n",
    "```\n",
    "\n",
    "Syntax:\n",
    "```\n",
    "    f = open(\"demofile.txt\")\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "File Not Found\n"
     ]
    }
   ],
   "source": [
    "try:\n",
    "    file = open(\"demo.txt\")\n",
    "    #or\n",
    "    #f = open(\"demo.txt\", \"r\") #r is for read mode which by default\n",
    "except:\n",
    "    print(\"File Not Found\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Lets create a demo file for further understandings.\n",
    "\n",
    "demofile.txt contains\n",
    "\n",
    "```\n",
    "    Hello! Welcome to demofile.txt\n",
    "    This file is for testing purposes.\n",
    "    Good Luck!\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<b> Open File </b>\n",
    "\n",
    "To open the file, use the built-in open() function.\n",
    "\n",
    "The open() function returns a file object, which has a read() method for reading the content of the file:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello! Welcome to demofile.txt\n",
      "This file is for testing purposes.\n",
      "Good Luck!\n"
     ]
    }
   ],
   "source": [
    "file = open(\"demofile.txt\", \"r\")\n",
    "print(file.read())"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello! Wel\n"
     ]
    }
   ],
   "source": [
    "file = open(\"demofile.txt\", \"r\")\n",
    "print(file.read(10)) #reads first 10 characters of file instead of whole text"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<b>Read lines </b>\n",
    "You can return one line by using the readline() method:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello! Welcome to demofile.txt\n",
      "\n"
     ]
    }
   ],
   "source": [
    "file = open(\"demofile.txt\", \"r\")\n",
    "print(file.readline())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "By looping through the lines of the file, you can read the whole file, line by line:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello! Welcome to demofile.txt\n",
      "\n",
      "This file is for testing purposes.\n",
      "\n",
      "Good Luck!\n"
     ]
    }
   ],
   "source": [
    "file = open(\"demofile.txt\",\"r\")\n",
    "\n",
    "for line in file:\n",
    "    print(line)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<b>Close File</b>\n",
    "\n",
    "It is a good practice to always close the file when you are done with it."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Hello! Welcome to demofile.txt\n",
      "\n",
      "This file is for testing purposes.\n",
      "\n",
      "Good Luck!\n"
     ]
    }
   ],
   "source": [
    "file = open(\"demofile.txt\",\"r\")\n",
    "\n",
    "for line in file:\n",
    "    print(line)\n",
    "    \n",
    "file.close()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<b>Note:</b> You should always close your files,\n",
    "in some cases, due to buffering, changes made to a file may not show until you close the file."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Writing to an existing file\n",
    "To write to an existing file, you must add a parameter to the open() function:\n",
    "```\n",
    "\"a\" - Append - will append to the end of the file\n",
    "\n",
    "\"w\" - Write - will overwrite any existing content\n",
    "\n",
    "\"x\" - Create - will create a file, returns an error if the file exist\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Append\n",
    "\n",
    "file = open(\"demofile.txt\", \"a\")\n",
    "file.write(\"\\nNow the file has more content!\") #\"\\n\" new line character in text/strings\n",
    "file.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [],
   "source": [
    "# write\n",
    "file = open(\"demofile.txt\",\"w\")\n",
    "file.write(\"Oops. I have deleted the content!\")\n",
    "file.close()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [],
   "source": [
    "# create\n",
    "\n",
    "f = open(\"myfile.txt\", \"x\") #file created"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Delete a file\n",
    "\n",
    "You can use OS module for removing file"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Deleting the requested file\n"
     ]
    }
   ],
   "source": [
    "import os\n",
    "if os.path.exists(\"demofile.txt\"):\n",
    "    print(\"Deleting the requested file\")\n",
    "    os.remove(\"demofile.txt\")\n",
    "else:\n",
    "    print(\"The file does not exist\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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