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   "source": [
    "### <center>San Jose State University<br>Department of Applied Data Science<br><br>**DATA 200<br>Computational Programming for Data Analytics**<br><br>Spring 2023<br>Instructor: Ron Mak</center>"
   ]
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   "source": [
    "# 9.4 Updating Text Files"
   ]
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   "metadata": {},
   "source": [
    "### Updating `accounts.txt` "
   ]
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   "source": [
    "def dump_textfile(file_name):\n",
    "    \"\"\"\n",
    "    accounts.read() returns the entire file contents\n",
    "    as a single string.\n",
    "    \"\"\"\n",
    "    textfile = open(file_name, mode='r')\n",
    "    print(textfile.read())\n",
    "    textfile.close()"
   ]
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  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "dump_textfile('accounts.txt')"
   ]
  },
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   "metadata": {},
   "source": [
    "#### Suppose we want to replace 'Jones' with 'Abernathy'."
   ]
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   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "# Read the entire contents of the file into a string.\n",
    "accounts = open('accounts.txt', mode='r')\n",
    "contents = accounts.read()\n",
    "accounts.close()\n",
    "\n",
    "# Modify the string.\n",
    "contents = contents.replace('Jones', 'Abernathy')\n",
    "\n",
    "# Write the modified contents to the file,\n",
    "# overwriting the original contents.\n",
    "accounts = open('accounts.txt', mode='w')\n",
    "accounts.write(contents)\n",
    "accounts.close()\n",
    "\n",
    "dump_textfile('accounts.txt')"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### If the file is large, we may not want to read all of its contents into a string. Instead, we can make a temporary copy of the file. When we reach the line we to modify, we can make the replacement. For example, replace 'White' with 'Williams' in account 300:"
   ]
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   "cell_type": "code",
   "execution_count": null,
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   "outputs": [],
   "source": [
    "accounts  = open('accounts.txt', 'r')\n",
    "temp_file = open('temp_file.txt', 'w')\n",
    "\n",
    "with accounts, temp_file:\n",
    "    for record in accounts:\n",
    "        account, name, balance = record.split()\n",
    "        \n",
    "        if account != '300':\n",
    "            temp_file.write(record)\n",
    "        else:\n",
    "            new_record = ' '.join([account, 'Williams', balance])\n",
    "            temp_file.write(new_record + '\\n')"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### `os` Module File Processing Functions"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Use the `os` (operating systems interface) module to remove file `accounts.txt` and rename file `temp_file.txt` to `accounts.txt`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import os"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "os.remove('accounts.txt')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "os.rename('temp_file.txt', 'accounts.txt')"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Command-Line Arguments\n",
    "#### If you run a standalone Python program from the command line, you can pass arguments to the program. For example:\n",
    "```\n",
    "ipython copy_file.py accounts.txt backup.txt\n",
    "```"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Your program can use the `sys` module to retrieve the values of the command-line arguments from the module's `argv` list. For example:\n",
    "``` python\n",
    "source_file_name = argv[0]\n",
    "target_file_name = argv[1]\n",
    "```"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "##########################################################################\n",
    "# (C) Copyright 2019 by Deitel & Associates, Inc. and                    #\n",
    "# Pearson Education, Inc. All Rights Reserved.                           #\n",
    "#                                                                        #\n",
    "# DISCLAIMER: The authors and publisher of this book have used their     #\n",
    "# best efforts in preparing the book. These efforts include the          #\n",
    "# development, research, and testing of the theories and programs        #\n",
    "# to determine their effectiveness. The authors and publisher make       #\n",
    "# no warranty of any kind, expressed or implied, with regard to these    #\n",
    "# programs or to the documentation contained in these books. The authors #\n",
    "# and publisher shall not be liable in any event for incidental or       #\n",
    "# consequential damages in connection with, or arising out of, the       #\n",
    "# furnishing, performance, or use of these programs.                     #\n",
    "##########################################################################\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Additional material (C) Copyright 2023 by Ronald Mak"
   ]
  }
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