Question

I’m new to python (and in any real sense) to programming. I’ve been playing around with this problem and here’s my extended solution to repeatedly check a whitelist file to see whether user input domains are whitelisted (one at a time). The whitelist file contains a list of domains (one per record).

It appears to work but I got there by trial and error. Can this be done in a more elegant, efficient and ‘pythonic’ manner? I’ve not got round to error checking yet (if that is relevant). Any tips gratefully received.

#!/usr/bin/env python3
# Filename: whitelist.py

domain = 1
match = 0
while domain:
    domain = input('Enter a domain or press return to exit: ') 
    if not domain: # if return is pressed entered then end program
        break
    with open('whitelist.txt', 'r', encoding='utf-8') as whitelist:
        for recd in whitelist: 
            # if input domain doesn't match record read next record (continue)
            if recd.lower().rstrip() != domain.lower():  
                continue
            else: # otherwise if match set match indicator
                match = 1
            break # after setting indicator stop reading records

        if match:
            print('Match on domain: ', domain)                
        else:   
            print('No match on: ', domain)

After taking on board larsmans’ comments my new solution is basically his solution with a slight change to make all checks use lower case (e.g. so cnn.com == CNN.com):

#!/usr/bin/env python3
# Filename: whitelist.py

with open('whitelist.txt', 'r', encoding='utf-8') as f:
    whitelist = set(line.lower().rstrip() for line in f) 

while True:
    domain = input('Enter a domain or press return to exit: ') 
    if not domain: 
        break

    if domain.lower() in whitelist:
        print('Match on domain: ', domain)                
    else:   
        print('No match on: ', domain)

Answer 1

for recd in whitelist: 
    # if input domain doesn't match record read next record (continue)
    if recd.lower().rstrip() != domain.lower():  
        continue
    else: # otherwise if match set match indicator
        match = 1
    break # after setting indicator stop reading records

can be written more succintly

for recd in whitelist:
    if recd.lower().rstrip() == domain.lower():
        match = 1
        break

Also, you should be using True and False for booleans, rather than 0 and 1.

Third, you should really be reading the whitelist file once, outside of the loop. Ideally, you’d read it into a set to allow for fast lookup.

with open("whitelist.txt") as f:
    whitelist = set(ln.rstrip() for ln in f)

Then the loop becomes

while True:
    domain = input('Enter a domain or press return to exit: ')
    if not domain:
        break

    if domain in whitelist:
        print('Match on domain: ', domain)                
    else:   
        print('No match on: ', domain)

Note that I’ve changed the loop condition to while True because the check for not domain already occurs inside it.