Update a file through Python Algorithm

Description:

In this project, I will be explaining a step-by-step process about how I was able to open a file, read the contents within the file, write contents within the file, and create an algorithm that can update a file using Python.

Scenario

I am a security professional working at a health care company. My job is to regularly update a file that identifies the employees who can access restricted content. The contents of the file are based on who is working with personal patient records. Employees are restricted access based on their IP address. There is an allow list of IP addresses permitted to sign into the restricted subnetwork. There's also a remove list that identifies which employees I must remove from this allow list. I created an algorithm to automate updating the "allow_list.txt" file and remove these IP addresses that should no longer have access.

Walkthrough:

Step 1: Open the file that contains the allow list

For the first part of the algorithm, I opened the allow_list.txt file. First, I assigned this file name as a string to the import_file variable:

# Create a variable 'import_file' which is assigned to the file location of the allowed list of users' IP addresses.
import_file = "/home/kali/allow_list.txt"

# A list of IP addresses that are no longer allowed to access restricted information. 
remove_list = ["192.168.97.225", "192.168.158.170", "192.168.201.40", "192.168.58.57"]

Then, I used a with statement to open the file:

# Build `with` statement to read in the initial contents of the file
with open(import_file, "r") as file:

The with statement is used with the .open() function in read mode so that it can open the allow_list.txt file and read the contents inside. There are two parameters that are happening inside the .open() function. One is the import_file, which identifies the file to import, and then the second indicates what type of mode I want to do with the file. In this case, "r" means I want to read the file. The code also uses the keyword as which assign a variable named file. file stores the output of the .open() function while I work within the with statement.

Step 2: Read the file contents

In order to read the file contents, I used the .read() method to convert it into a string.

import_file = "/home/kali/allow_list.txt"

with open(import_file, "r") as file:

  # Use `.read()` to read the important file and store it in a variable named `ip_addresses`
  ip_addresses = file.read()

print(ip_addresses)

I am using the .read() function which is used in the body of the with statement. The .read() method converts the file into a string and allows me to read it. I applied the .read() method to the file variable identified in the with statement. Then, I assigned the string output of this method to the variable ip_addresses.

Furthermore, this code reads the contents of the "allow_list.txt file into a string format that allows me to later use the string to organize and extract data in my Python program. Here's the output of what it is when I read the file.

# Output for reading allow_list.txt
192.168.25.60
192.168.205.12
192.168.97.225
192.168.6.9
192.168.52.90
192.168.158.170
192.168.90.124
192.168.186.176
192.168.133.188
192.168.203.198
192.168.201.40
192.168.218.219
192.168.52.37
192.168.156.224
192.168.60.153
192.168.58.57
192.168.69.116

Step 3: Convert the string into a list

In order to remove individual IP addresses from the allow list, I need it to be in list format. Therefore, I next used the .split() method to convert the ip_addresses string into a list:

# Create a variable 'import_file' which is assigned to the file location of the allowed list of users' IP addresses.
import_file = "/home/kali/allow_list.txt"

# A list of IP addresses that are no longer allowed to access restricted information. 
remove_list = ["192.168.97.225", "192.168.158.170", "192.168.201.40", "192.168.58.57"]

# Build `with` statement to read in the initial contents of the file

with open(import_file, "r") as file:

    # Use `.read()` to read the imported file and store it in a variable named `ip_addresses`

    ip_addresses = file.read()

# Use `.split()` to convert `ip_addresses` from a string to a list

ip_addresses = ip_addresses.split()

# Display `ip_addresses`

print(ip_addresses)

The .split() function is called by appending it to a string variable. It works by converting the contents of a string to a list. The purpose of splitting ip_addresses into a list is to make it easier to remove IP addresses from the allow list. By default, the .split() function splits the text by whitespace into list elements. In this algorithm, the .split() function takes the data stored in the variable ip_addresses, which is a string of IP addresses that are each separated by a whitespace, and it converts this string into a list of IP addresses. To store this list, I reassigned it back to the variable ip_addresses.

Here's what the output will be like when I convert a string into a list.

# Output

['192.168.25.60', '192.168.205.12', '192.168.97.225', '192.168.6.9', '192.168.52.90', '192.168.158.170', '192.168.90.124', '192.168.186.176', '192.168.133.188',
'192.168.203.198', '192.168.201.40', '192.168.218.219', '192.168.52.37', '192.168.156.224', '192.168.60.153', '192.168.58.57', '192.168.69.116']

Step 4: Iterate through the remove list

The next step for me to do is to iterate through the IP addresses that are elements in the remove_list. To do this, I incorporated a for loop:

# Build iterative statement
# Name loop variable `element`
# Loop through `remove_list`

for element in remove_list:

The for loop in Python repeats code for a specified sequence. The overall purpose of the for loop in a Python algorithm like this is to apply specific code statements to all elements in a sequence. The keyword element will iterate through each of the ip_addresses in the remove_list.

Step 5: Remove IP addresses that are on the remove list

In this step, I will create an if statement inside the for loop of the remove_list, which will check and see if the remove list has any matching pairs with the allow_list. If it does then it will remove those IP addresses with the .remove() method.

. This will check if there are any ip_addreses from the allow list that match with the remove_list. If it does match, I will use the .remove() method which will remove any duplicate IP addresses.

for element in remove_list:
  
  # Create a conditional statement to evaluate if `element` is in `ip_addresses`

  if element in ip_addresses:
      
      ip_addresses.remove(element)


# Display `ip_addresses`

print(ip_addresses)

Here's what the output looks like:

# List of IP addresses that need to be removed
192.168.97.225
192.168.158.170
192.168.201.40
192.168.58.57

# List of IP addresses that are in allow_list and have been removed from the `remove_list`.
['192.168.25.60', '192.168.205.12', '192.168.6.9', '192.168.52.90', '192.168.90.124', '192.168.186.176', '192.168.133.188',
'192.168.203.198', '192.168.218.219', '192.168.52.37', '192.168.156.224', '192.168.60.153', '192.168.69.116']

Step 6: Update the file with the revised list of IP addresses

As a final step in my algorithm, I needed to update the allow list file with the revisited list of IP addresses. To do so, I first needed to convert the list back into a string. I used the .join() method for this.

# Convert `ip_addresses` back to a string so that it can be written into the text file

ip_addresses = "\n".join(ip_addresses)

Now it should return back into a column that lists each IP address as before, but revised.

192.168.25.60
192.168.205.12
192.168.6.9
192.168.52.90
192.168.90.124
192.168.186.176
192.168.133.188
192.168.203.198
192.168.218.219
192.168.52.37
192.168.156.224
192.168.60.153
192.168.69.116

The .join() method combines all items in an iterable into a string. The .join() method is applied to a string containing characters that will separate the elements in the iterable once joined into a string. In this algorithm, I used the .join() method to create a string from the list ip_addresses so that I could pass it in as an argument to the .write() method when writing to the file "allow_list.txt". I used the string ("\n") as the separator to instruct Python to place each element on a new line.

Here's where I update the file using the .write() method which will update this file:

# Build `with` statement to rewrite the original file

with open(import_file, "w") as file:

  # Rewrite the file, replacing its contents with `ip_addresses`

  file.write(ip_addresses)

This will make the file allow_list.txt into a newly reformed list of IP addresses that I have just overwritten with Python.

Step 7: Finalize code and create a function

Now this is where I bring all the steps together into one function called, update_file. This function will be passed by two parameters: import_file and remove_list

# Create a variable 'import_file' which is assigned to the file location of the allowed list of users' IP addresses.
import_file = "/home/kali/allow_list.txt"

# A list of IP addresses that are no longer allowed to access restricted information. 
remove_list = ["192.168.97.225", "192.168.158.170", "192.168.201.40", "192.168.58.57"]

def update_file(import_file, remove_list):

  # Build `with` statement to read in the initial contents of the file

  with open(import_file, "r") as file:

      # Use `.read()` to read the imported file and store it in a variable named `ip_addresses`

      ip_addresses = file.read()

  # Use `.split()` to convert `ip_addresses` from a string to a list

  ip_addresses = ip_addresses.split()

  # Build iterative statement
  # Name loop variable `element`
  # Loop through `remove_list`

  for element in remove_list:
  
      # Create a conditional statement to evaluate if `element` is in `ip_addresses`

      if element in ip_addresses:

          # use the `.remove()` method to remove
          # elements from `ip_addresses`

          ip_addresses.remove(element)

  # Convert `ip_addresses` back to a string so that it can be written into the text file

  ip_addresses = "\n".join(ip_addresses)

  # Build `with` statement to rewrite the original file

  with open(import_file, "w") as file:

      # Rewrite the file, replacing its contents with `ip_addresses`

      file.write(ip_addresses)

  # Call `update_file()` and pass in "allow_list.txt" and a list of IP addresses to be removed
  
  update_file(import_file, remove_list)
  
  # Build `with` statement to read in the updated file
  
  with open("allow_list.txt", "r") as file:
  
      # Read in the updated file and store the contents in `text`
  
      text = file.read()
  
  # Display the contents of `text`
  
  print(text)

Summary

From the "allow_list.txt" file of authorized IP addresses, I developed an algorithm that eliminates IP addresses listed in a remove_list variable. This procedure comprised opening the file, reading the string it was converted into, and then transforming the list into the variable ip_addresses. I next went through the IP addresses in remove_list iteratively. I determined each time whether the entry was a part of the ip_addresses list. If so, I used the .remove() method to take the entry out of ip_addresses. Then, in order to replace the IP address list in the "allow_list.txt" file with the updated list, I used the .join() technique to turn the IP addresses back into strings.