PY0101EN-4-2-WriteFile.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<p style=\"text-align:center\">\n",
    "    <a href=\"https://skills.network/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\" target=\"_blank\">\n",
    "    <img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/assets/logos/SN_web_lightmode.png\" width=\"200\" alt=\"Skills Network Logo\"  />\n",
    "    </a>\n",
    "</p>\n",
    "\n",
    "# Write and Save Files in Python\n",
    "\n",
    "Estimated time needed: **25** minutes\n",
    "\n",
    "## Objectives\n",
    "\n",
    "After completing this lab you will be able to:\n",
    "\n",
    "*   Write to files using Python libraries\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<h2>Table of Contents</h2>\n",
    "<div class=\"alert alert-block alert-info\" style=\"margin-top: 20px\">\n",
    "    <ul>\n",
    "        <li><a href=\"https://write/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\">Writing Files</a></li>\n",
    "        <li><a href=\"https://append/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\">Appending Files</a></li>\n",
    "        <li><a href=\"https://add/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\">Additional File modes</a></li>\n",
    "        <li><a href=\"https://copy/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\">Copy a File</a></li>\n",
    "    </ul>\n",
    "\n",
    "</div>\n",
    "\n",
    "<hr>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<h2 id=\"write\">Writing Files</h2>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can open a file object using the method <code>write()</code> to save the text file to a list. To write to a file, the mode argument must be set to **w**. Let’s write a file **Example2.txt** with the line: **“This is line A”**\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: '/resources/data/Example2.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m~\\AppData\\Local\\Temp/ipykernel_11240/2359273157.py\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# Write line to file\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[0mexmp2\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'/resources/data/Example2.txt'\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[1;32mwith\u001b[0m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mexmp2\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'w'\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mwritefile\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      4\u001b[0m     \u001b[0mwritefile\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mwrite\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"This is line A\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: '/resources/data/Example2.txt'"
     ]
    }
   ],
   "source": [
    "# Write line to file\n",
    "exmp2 = '/resources/data/Example2.txt'\n",
    "with open(exmp2, 'w') as writefile:\n",
    "    writefile.write(\"This is line A\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can read the file to see if it worked:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: '/resources/data/Example2.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m~\\AppData\\Local\\Temp/ipykernel_11240/2863215952.py\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# Read file\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[1;32mwith\u001b[0m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mexmp2\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'r'\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mtestwritefile\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      4\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mtestwritefile\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mread\u001b[0m\u001b[1;33m(\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[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: '/resources/data/Example2.txt'"
     ]
    }
   ],
   "source": [
    "# Read file\n",
    "\n",
    "with open(exmp2, 'r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can write multiple lines:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: '/resources/data/Example2.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m~\\AppData\\Local\\Temp/ipykernel_11240/1989772125.py\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# Write lines to file\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[1;32mwith\u001b[0m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mexmp2\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'w'\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mwritefile\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      4\u001b[0m     \u001b[0mwritefile\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mwrite\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"This is line A\\n\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      5\u001b[0m     \u001b[0mwritefile\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mwrite\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"This is line B\\n\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: '/resources/data/Example2.txt'"
     ]
    }
   ],
   "source": [
    "# Write lines to file\n",
    "\n",
    "with open(exmp2, 'w') as writefile:\n",
    "    writefile.write(\"This is line A\\n\")\n",
    "    writefile.write(\"This is line B\\n\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The method <code>.write()</code> works similar to the method <code>.readline()</code>, except instead of reading a new line it writes a new line. The process is illustrated in the figure. The different colour coding of the grid represents a new line added to the file after each method call.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/images/WriteLine.png\" width=\"500\" />\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can check the file to see if your results are correct\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "ename": "FileNotFoundError",
     "evalue": "[Errno 2] No such file or directory: '/resources/data/Example2.txt'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mFileNotFoundError\u001b[0m                         Traceback (most recent call last)",
      "\u001b[1;32m~\\AppData\\Local\\Temp/ipykernel_11240/4182224387.py\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# Check whether write to file\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      2\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 3\u001b[1;33m \u001b[1;32mwith\u001b[0m \u001b[0mopen\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mexmp2\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;34m'r'\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;32mas\u001b[0m \u001b[0mtestwritefile\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      4\u001b[0m     \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mtestwritefile\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mread\u001b[0m\u001b[1;33m(\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[1;31mFileNotFoundError\u001b[0m: [Errno 2] No such file or directory: '/resources/data/Example2.txt'"
     ]
    }
   ],
   "source": [
    "# Check whether write to file\n",
    "\n",
    "with open(exmp2, 'r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We write a list to a **.txt** file  as follows:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "['This is line A\\n', 'This is line B\\n', 'This is line C\\n']"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Sample list of text\n",
    "\n",
    "Lines = [\"This is line A\\n\", \"This is line B\\n\", \"This is line C\\n\"]\n",
    "Lines"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "This is line A\n",
      "\n",
      "This is line B\n",
      "\n",
      "This is line C\n",
      "\n"
     ]
    }
   ],
   "source": [
    "# Write the strings in the list to text file\n",
    "\n",
    "with open('Example2.txt', 'w') as writefile:\n",
    "    for line in Lines:\n",
    "        print(line)\n",
    "        writefile.write(line)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can verify the file is written by reading it and printing out the values:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "This is line A\n",
      "This is line B\n",
      "This is line C\n",
      "\n"
     ]
    }
   ],
   "source": [
    "# Verify if writing to file is successfully executed\n",
    "\n",
    "with open('Example2.txt', 'r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "However, note that setting the mode to **w** overwrites all the existing data in the file.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwrite\n",
      "\n"
     ]
    }
   ],
   "source": [
    "with open('Example2.txt', 'w') as writefile:\n",
    "    writefile.write(\"Overwrite\\n\")\n",
    "with open('Example2.txt', 'r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "<h2 id=\"Append\">Appending Files</h2>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can write to files without losing any of the existing data as follows by setting the mode argument to append: **a**.  you can append a new line as follows:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Write a new line to text file\n",
    "\n",
    "with open('Example2.txt', 'a') as testwritefile:\n",
    "    testwritefile.write(\"This is line C\\n\")\n",
    "    testwritefile.write(\"This is line D\\n\")\n",
    "    testwritefile.write(\"This is line E\\n\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "You can verify the file has changed by running the following cell:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwrite\n",
      "This is line C\n",
      "This is line D\n",
      "This is line E\n",
      "\n"
     ]
    }
   ],
   "source": [
    "# Verify if the new line is in the text file\n",
    "\n",
    "with open('Example2.txt', 'r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "<h2 id=\"add\">Additional modes</h2> \n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "It's fairly ineffecient to open the file in **a** or **w** and then reopening it in **r** to read any lines. Luckily we can access the file in the following modes:\n",
    "\n",
    "*   **r+** : Reading and writing. Cannot truncate the file.\n",
    "*   **w+** : Writing and reading. Truncates the file.\n",
    "*   **a+** : Appending and Reading. Creates a new file, if none exists.\n",
    "\n",
    "You dont have to dwell on the specifics of each mode for this lab.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let's try out the **a+** mode:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "\n"
     ]
    }
   ],
   "source": [
    "with open('Example2.txt', 'a+') as testwritefile:\n",
    "    testwritefile.write(\"This is line E\\n\")\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "There were no errors but <code>read()</code> also did not output anything. This is because of our location in the file.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Most of the file methods we've looked at work in a certain location in the file. <code>.write() </code> writes at a certain location in the file. <code>.read()</code> reads at a certain location in the file and so on. You can think of this as moving your pointer around in the notepad to make changes at specific location.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Opening the file in **w** is akin to opening the .txt file, moving your cursor to the beginning of the text file, writing new text and deleting everything that follows.\n",
    "Whereas opening the file in **a** is similiar to opening the .txt file, moving your cursor to the very end and then adding the new pieces of text. <br>\n",
    "It is often very useful to know where the 'cursor' is in a file and be able to control it. The following methods allow us to do precisely this -\n",
    "\n",
    "*   <code>.tell()</code> - returns the current position in bytes\n",
    "*   <code>.seek(offset,from)</code> - changes the position by 'offset' bytes with respect to 'from'. From can take the value of 0,1,2 corresponding to beginning, relative to current position and end\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now lets revisit **a+**\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Initial Location: 75\n",
      "Read nothing\n",
      "\n",
      "New Location : 0\n",
      "Overwrite\n",
      "This is line C\n",
      "This is line D\n",
      "This is line E\n",
      "This is line E\n",
      "\n",
      "Location after read: 75\n"
     ]
    }
   ],
   "source": [
    "with open('Example2.txt', 'a+') as testwritefile:\n",
    "    print(\"Initial Location: {}\".format(testwritefile.tell()))\n",
    "    \n",
    "    data = testwritefile.read()\n",
    "    if (not data):  #empty strings return false in python\n",
    "            print('Read nothing') \n",
    "    else: \n",
    "            print(testwritefile.read())\n",
    "            \n",
    "    testwritefile.seek(0,0) # move 0 bytes from beginning.\n",
    "    \n",
    "    print(\"\\nNew Location : {}\".format(testwritefile.tell()))\n",
    "    data = testwritefile.read()\n",
    "    if (not data): \n",
    "            print('Read nothing') \n",
    "    else: \n",
    "            print(data)\n",
    "    \n",
    "    print(\"Location after read: {}\".format(testwritefile.tell()) )"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Finally, a note on the difference between **w+** and **r+**. Both of these modes allow access to read and write methods, however, opening a file in **w+** overwrites it and deletes all pre-existing data. <br>\n",
    "To work with a file on existing data, use **r+** and **a+**. While using **r+**, it can be useful to add a <code>.truncate()</code> method at the end of your data. This will reduce the file to your data and delete everything that follows. <br>\n",
    "In the following code block, Run the code as it is first and then run it with the <code>.truncate()</code>.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Line 1\n",
      "Line 2\n",
      "Line 3\n",
      "finished\n",
      " line D\n",
      "This is line E\n",
      "This is line E\n",
      "\n"
     ]
    }
   ],
   "source": [
    "with open('Example2.txt', 'r+') as testwritefile:\n",
    "    data = testwritefile.readlines()\n",
    "    testwritefile.seek(0,0) #write at beginning of file\n",
    "   \n",
    "    testwritefile.write(\"Line 1\" + \"\\n\")\n",
    "    testwritefile.write(\"Line 2\" + \"\\n\")\n",
    "    testwritefile.write(\"Line 3\" + \"\\n\")\n",
    "    testwritefile.write(\"finished\\n\")\n",
    "    #Uncomment the line below\n",
    "    #testwritefile.truncate()\n",
    "    testwritefile.seek(0,0)\n",
    "    print(testwritefile.read())\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<h2 id=\"copy\">Copy a File</h2> \n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Let's copy the file **Example2.txt** to the file **Example3.txt**:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Copy file to another\n",
    "\n",
    "with open('Example2.txt','r') as readfile:\n",
    "    with open('Example3.txt','w') as writefile:\n",
    "          for line in readfile:\n",
    "                writefile.write(line)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "We can read the file to see if everything works:\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Line 1\n",
      "Line 2\n",
      "Line 3\n",
      "finished\n",
      " line D\n",
      "This is line E\n",
      "This is line E\n",
      "\n"
     ]
    }
   ],
   "source": [
    "# Verify if the copy is successfully executed\n",
    "\n",
    "with open('Example3.txt','r') as testwritefile:\n",
    "    print(testwritefile.read())"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "After reading files, we can also write data into files and save them in different file formats like **.txt, .csv, .xls (for excel files) etc**. You will come across these in further examples\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**NOTE:** If you wish to open and view the `example3.txt` file, download this lab [here](https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/PY0101EN-4-2-WriteFile.ipynb) and run it locally on your machine. Then go to the working directory to ensure the `example3.txt` file exists and contains the summary data that we wrote.\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<h2> Exercise </h2>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Your local university's Raptors fan club maintains a register of its active members on a .txt document. Every month they update the file by removing the members who are not active. You have been tasked with automating this with your Python skills. <br>\n",
    "Given the file `currentMem`, Remove each member with a 'no' in their Active column. Keep track of each of the removed members and append them to the `exMem` file. Make sure that the format of the original files in preserved.   (*Hint: Do this by reading/writing whole lines and ensuring the header remains* ) <br>\n",
    "Run the code block below prior to starting the exercise. The skeleton code has been provided for you. Edit only the `cleanFiles` function.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "metadata": {},
   "outputs": [],
   "source": [
    "#Run this prior to starting the exercise\n",
    "from random import randint as rnd\n",
    "\n",
    "memReg = 'members.txt'\n",
    "exReg = 'inactive.txt'\n",
    "fee =('yes','no')\n",
    "\n",
    "def genFiles(current,old):\n",
    "    with open(current,'w+') as writefile: \n",
    "        writefile.write('Membership No  Date Joined  Active  \\n')\n",
    "        data = \"{:^13}  {:<11}  {:<6}\\n\"\n",
    "\n",
    "        for rowno in range(20):\n",
    "            date = str(rnd(2015,2020))+ '-' + str(rnd(1,12))+'-'+str(rnd(1,25))\n",
    "            writefile.write(data.format(rnd(10000,99999),date,fee[rnd(0,1)]))\n",
    "\n",
    "\n",
    "    with open(old,'w+') as writefile: \n",
    "        writefile.write('Membership No  Date Joined  Active  \\n')\n",
    "        data = \"{:^13}  {:<11}  {:<6}\\n\"\n",
    "        for rowno in range(3):\n",
    "            date = str(rnd(2015,2020))+ '-' + str(rnd(1,12))+'-'+str(rnd(1,25))\n",
    "            writefile.write(data.format(rnd(10000,99999),date,fee[1]))\n",
    "\n",
    "\n",
    "genFiles(memReg,exReg)\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Now that you've run the prerequisite code cell above, which prepared the files for this exercise, you are ready to move on to the implementation.\n",
    "\n",
    "#### **Exercise:** Implement the cleanFiles function in the code cell below.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "  \n",
    "'''\n",
    "The two arguments for this function are the files:\n",
    "    - currentMem: File containing list of current members\n",
    "    - exMem: File containing list of old members\n",
    "    \n",
    "    This function should remove all rows from currentMem containing 'no' \n",
    "    in the 'Active' column and appends them to exMem.\n",
    "    '''\n",
    "def cleanFiles(currentMem, exMem):\n",
    "    # TODO: Open the currentMem file as in r+ mode\n",
    "        #TODO: Open the exMem file in a+ mode\n",
    "\n",
    "        #TODO: Read each member in the currentMem (1 member per row) file into a list.\n",
    "        # Hint: Recall that the first line in the file is the header.\n",
    "\n",
    "        #TODO: iterate through the members and create a new list of the innactive members\n",
    "\n",
    "        # Go to the beginning of the currentMem file\n",
    "        # TODO: Iterate through the members list. \n",
    "        # If a member is inactive, add them to exMem, otherwise write them into currentMem\n",
    "\n",
    "        \n",
    "    \n",
    "    pass # Remove this line when done implementation\n",
    "\n",
    "\n",
    "# The code below is to help you view the files.\n",
    "# Do not modify this code for this exercise.\n",
    "memReg = 'members.txt'\n",
    "exReg = 'inactive.txt'\n",
    "cleanFiles(memReg,exReg)\n",
    "\n",
    "\n",
    "headers = \"Membership No  Date Joined  Active  \\n\"\n",
    "with open(memReg,'r') as readFile:\n",
    "    print(\"Active Members: \\n\\n\")\n",
    "    print(readFile.read())\n",
    "    \n",
    "with open(exReg,'r') as readFile:\n",
    "    print(\"Inactive Members: \\n\\n\")\n",
    "    print(readFile.read())\n",
    "                \n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "The code cell below is to verify your solution. Please do not modify the code and run it to test your implementation of `cleanFiles`.\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "def testMsg(passed):\n",
    "    if passed:\n",
    "       return 'Test Passed'\n",
    "    else :\n",
    "       return 'Test Failed'\n",
    "\n",
    "testWrite = \"testWrite.txt\"\n",
    "testAppend = \"testAppend.txt\" \n",
    "passed = True\n",
    "\n",
    "genFiles(testWrite,testAppend)\n",
    "\n",
    "with open(testWrite,'r') as file:\n",
    "    ogWrite = file.readlines()\n",
    "\n",
    "with open(testAppend,'r') as file:\n",
    "    ogAppend = file.readlines()\n",
    "\n",
    "try:\n",
    "    cleanFiles(testWrite,testAppend)\n",
    "except:\n",
    "    print('Error')\n",
    "\n",
    "with open(testWrite,'r') as file:\n",
    "    clWrite = file.readlines()\n",
    "\n",
    "with open(testAppend,'r') as file:\n",
    "    clAppend = file.readlines()\n",
    "        \n",
    "# checking if total no of rows is same, including headers\n",
    "\n",
    "if (len(ogWrite) + len(ogAppend) != len(clWrite) + len(clAppend)):\n",
    "    print(\"The number of rows do not add up. Make sure your final files have the same header and format.\")\n",
    "    passed = False\n",
    "    \n",
    "for line in clWrite:\n",
    "    if  'no' in line:\n",
    "        passed = False\n",
    "        print(\"Inactive members in file\")\n",
    "        break\n",
    "    else:\n",
    "        if line not in ogWrite:\n",
    "            print(\"Data in file does not match original file\")\n",
    "            passed = False\n",
    "print (\"{}\".format(testMsg(passed)))\n",
    "    \n",
    "\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<details><summary>Click here for the solution</summary>\n",
    "\n",
    "```python\n",
    "def cleanFiles(currentMem,exMem):\n",
    "    with open(currentMem,'r+') as writeFile: \n",
    "        with open(exMem,'a+') as appendFile:\n",
    "            #get the data\n",
    "            writeFile.seek(0)\n",
    "            members = writeFile.readlines()\n",
    "            #remove header\n",
    "            header = members[0]\n",
    "            members.pop(0)\n",
    "                \n",
    "            inactive = [member for member in members if ('no' in member)]\n",
    "            '''\n",
    "            The above is the same as \n",
    "\n",
    "            for member in members:\n",
    "            if 'no' in member:\n",
    "                inactive.append(member)\n",
    "            '''\n",
    "            #go to the beginning of the write file\n",
    "            writeFile.seek(0) \n",
    "            writeFile.write(header)\n",
    "            for member in members:\n",
    "                if (member in inactive):\n",
    "                    appendFile.write(member)\n",
    "                else:\n",
    "                    writeFile.write(member)      \n",
    "            writeFile.truncate()\n",
    "                \n",
    "memReg = 'members.txt'\n",
    "exReg = 'inactive.txt'\n",
    "cleanFiles(memReg,exReg)\n",
    "\n",
    "# code to help you see the files\n",
    "\n",
    "headers = \"Membership No  Date Joined  Active  \\n\"\n",
    "\n",
    "with open(memReg,'r') as readFile:\n",
    "    print(\"Active Members: \\n\\n\")\n",
    "    print(readFile.read())\n",
    "    \n",
    "with open(exReg,'r') as readFile:\n",
    "    print(\"Inactive Members: \\n\\n\")\n",
    "    print(readFile.read())\n",
    "    \n",
    "```\n",
    "\n",
    "</details>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "<hr>\n",
    "<h2>The last exercise!</h2>\n",
    "<p>Congratulations, you have completed this lesson and hands-on lab in Python. \n",
    "<hr>\n"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Author\n",
    "\n",
    "<a href=\"https://www.linkedin.com/in/joseph-s-50398b136/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\" target=\"_blank\">Joseph Santarcangelo</a>\n",
    "\n",
    "### Other Contributors\n",
    "\n",
    "<a href=\"https://www.linkedin.com/in/jiahui-mavis-zhou-a4537814a?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2022-01-01\">Mavis Zhou</a>\n",
    "\n",
    "## Change Log\n",
    "\n",
    "| Date (YYYY-MM-DD) | Version | Changed By  | Change Description                  |\n",
    "| ----------------- | ------- | ----------- | ----------------------------------- |\n",
    "| 2022-01-10        | 2.1     | Malika      | Removed the readme for GitShare     |\n",
    "| 2020-10-16        | 1.3     | Arjun Swani | Added exercise                      |\n",
    "| 2020-10-16        | 1.2     | Arjun Swani | Added section additional file modes |\n",
    "| 2020-10-16        | 1.1     | Arjun Swani | Made append a different section     |\n",
    "| 2020-08-28        | 0.2     | Lavanya     | Moved lab to course repo in GitLab  |\n",
    "\n",
    "<hr>\n",
    "\n",
    "## <h3 align=\"center\"> © IBM Corporation 2020. All rights reserved. <h3/>\n"
   ]
  }
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