edit|version=40|last update=11:06:15 [CST] on 2026-09-21
Project description
This script updates a file called allow_list.txt to remove ips that are listed in a list called remove_list. We iterate through remove_list and use the .remove() method to remove them from the list we read in from the allow_list.txt file.
The file read gives us a string which we split into a list, making it easy to iterate through. After removing the ips frolm the remove_list, we recombine the list of ip_addresses into a single string and write it back out to the allow_list.txt file.
Open the file that contains the allow list
with open("allow_list.txt",'r')as file:
This code uses the with open() construct to open the file given in read mode and assigns the file object to the variable named file. Using with makes the program close the file as soon as the block is complete.
Read the file contents
ip_addresses=file.read()
This line of code reads the file opened in the previous line into the variable named ip_addresses using the read() method on the file object (contained in the variable named file)
Convert the string into a list
ip_addresses=ip_addresses.split()
This line of code uses the split() method on the string variable, ip_addresses to split the lines by linefeed and reassigns the list that produces back to ip_addresses. The default action of split is to split on the end of lines, although another character to split on can be used.
Iterate through the remove list
for element in remove_list:
This line of code sets up a loop to go thru the ip addresses in the list, remove_list, so they can be removed from the list
of ip addresses we loaded from the allow_list.txt file in previous steps. In each iteration through remove_list, the variable element is set to the next item in the remove_list list.
Remove IP addresses that are on the remove list
if element in ip_addresses:
ip_addresses.remove(element)
These lines of code check if element is in the list, ip_addresses, and if it is, them it removes element from the list using the .remove() method on the list object, ip_addresses. Using .remove() is possible since there are no duplicates in the list, ip_addresses. Otherwise, if there were duplicates, we'd have to .remove() once for each copy in the list.
Update the file with the revised list of IP addresses
ip_addresses.join("\n")
with open("allow_list.txt",'w') as file:
file.write(ip_addresses)
These lines of code allow us to recombine the lines in the ip_addresses list and write them back out to the file. No record of the removed ips is made so the change is permanent and irrevocable. 'w' is the argument to use to write a file. Using with open closes the file object after the block is done.
Summary
In summary, we had a list of ips we didn't want on the allow_list in a list called remove_list. We opened the allow_list.txt file and read in the existing ips. We saved the string containing all the ips in ip_addresses. Then we split that string by line and put the list of ips back into the same variable, making it easy to iterate through. Then we iterated through the list of ips in the remove_list and used the .remove() method to remove them from the ip_addresses list. After recombining the final list of ips without those on the remove_list using the .join() method, we wrote them back out to the allow_list.txt file using the with open() construct again so that the file object was closed after we finished.