Algorithm for file update in Python

Description: An algorithm that updates a file that identifies employees who can access restricted content. The restrictions are based on their IP address. There is an allow list for IP addresses permitted to sign into a restricted subnetwork. There is also a remove list that identifies which employees must be removed from the allow list.

Open the file that contains the allow list

In the code block below I needed to open a file called allow_list.txt. To do this I first assign a string containing this file name to a variable called import_file. Then using the with statement along with the open function containing the parameter keyword of “r” which tells the function that the file should be read. While working in the with statement the text is stored in a variable called file.

python-file-update/file_update_algorithm.py

Lines 1 to 11 in 41c274f

	# Assign `import_file` to the name of the file
	import_file = "allow_list.txt"
	# Assign `remove_list` to 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"]
	# First line of 'with' statement
	with open(import_file, "r") as file:

Read the file contents

To read the content of the file I had to use the .read() method to convert the contents of the “allow_list” file to a string, then store this string in a variable called ip_addresses.

python-file-update/file_update_algorithm.py

Lines 13 to 15 in 41c274f

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

Convert the string into a list

In order to remove individual IP addresses from the allow list, the IP addresses need to be in a list format. To do this I use the .split() method to convert the ip_addresses string into a list. Code below displays this.

python-file-update/file_update_algorithm.py

Lines 17 to 19 in 41c274f

	# Use 'split()' function to convert 'ip_addresses' from a string to a list
	ip_addresses = ip_addresses.split()

Iterate through the remove list

A second list called remove_list contains all of the IP addresses that should be removed from the ip_addresses list. The code below shows the header of a for loop that will iterate through the remove_list and use element as the loop variable.

python-file-update/file_update_algorithm.py

Lines 21 to 26 in 41c274f

	# Build interative statement
	# NAme loop variable 'element'
	# Loop through 'ip_addresses'
	for element in ip_addresses:

Remove IP addresses that are on the remove list

The code below will remove all the IP addresses from the allow list that are also on the remove list. This is done by first creating a conditional statement that evaluates if the loop variable element is part of the ip_addresses list. Then, within that conditional, apply the .remove() method to the ip_addresses list and remove the IP addresses identified in the loop variable element.

python-file-update/file_update_algorithm.py

Lines 28 to 35 in 41c274f

	# If current element is in 'remove_list',
	if element in remove_list:
	# then current element should be removed from 'ip_address'
	ip_addresses.remove(element)

Update the file with the revised list of IP addresses

Next, updating the file with this revised list. To do this, I first convert the ip_addresses list back into a string using the .join() method. Apply .join() to the string "\n" in order to separate the elements in the file by placing them on a new line. Using another with statement with “w” argument that tells the open() function that you are writing to the file. Then utilizing the .write() method to write over the file assigned to the import_file variable.

python-file-update/file_update_algorithm.py

Lines 36 to 46 in 41c274f

	# Convert 'ip_addresses' back to string so that so that it can 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 content with 'ip_addresses'
	file.write(ip_addresses)

Summary of Algorithm

Important

I created an algorithm that uses Python code to check whether a file of authorized IP addresses stored in a file called “allowed_list.txt” contained any unautorized IP addresses. These unauthorized IP addresses were stored in a remove_list variable and checked against the allowed list. If found in the allowed list those unauthorized IP addresses were removed from the file containing the allowed IP addresses.

• This was done by opening the file,
• converting it to a string to be read,
• then converting this string to a list stored in a variable called ip_addresses.
• The program iterated through the ip_addresses list, checking if the element of remove_list was a part of the list.
• If it was, it applied the .remove() method to remove the element from the ip_addresses list.
• Once completed the .join() method was used to convert the list back to a string so it could write over the content of the allow_list.txt file.