looking for a better solution to my script (python)

Question

so I wasn't sure how to phrase this in a search so I will give you the details. I'm using an nfc reader and if a card is found an action is performed. What I want to do is add a part where if the card is not in the database print "unknown card"

heres my script essentially. max = sum of lines in a text file cardid = card uid #

for i in range(max)
    with open(....) as file
        card = file.readlines()[i]
    if cardid == card
        print "card found"

that is pretty much what i have so far. it works as expected. The only workaround I can see is adding a variable 'cardfound' and doing this

cardfound = 0
for i in range(max)
    with open(....) as file
        card = file.readlines()[i]
    if cardid == card
        print "card found"
        cardfound = 1
if cardfound == 0
     print "unknown card"

is there a better method?

Amadan · Accepted Answer · 2014-08-27 05:55:55Z

3

First of all, you're reading the file over and over and over. Reading it once should suffice.

As for the rest - in most languages you would have to do basically what you did, have a flag somewhere that keeps track if you found something or not. However, Python has a cool for...else form:

with open(....) as file:
    for card in file.readlines():
        if card == cardid:
            print "OKAY!!!"
            break
    else:
        print "Sad now."

answered Aug 27, 2014 at 5:55

Amadan

200k23 gold badges253 silver badges321 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

kecer Over a year ago

Python has for...else form? That is neat. +1, Never heard of that

joegone Over a year ago

Hmm I will try the for else to see what happens. my file that I am opening contains 100 different id #. Each listed per line in the file. It is important I know which line contains the cardid. so if card id is the 13th one it will print "13".

aquavitae · Accepted Answer · 2014-08-27 12:25:09Z

2

I assume that if a card is found, you don't need to continue processing the file? In that case you can do this:

with open(....) as file
    for card in file.readlines()
        if cardid == card
            print "card found"
            break
    else:
        print "unknown card"

Note that the with open() line is outside the loop, you don't really want to open the file every time. Also, you can do away with the range(max) since file is an iterable.

If you do want to process the entire file (e.g. counting the number of cards found, then the way you are doing it is probably best, although it would be better style to use a boolean:

cardfound = False
with open(....) as file
    for card in file.readlines()
        if cardid == card
            print "card found"
            cardfound = True
if not cardfound:
     print "No card found"

Update If you want to count the lines, then rather than manually iterating over each line, count them using enumerate:

cardfound = False
with open(....) as file
    for i, card in enumerate(file.readlines())
        if cardid == card
            print "card found on line %d" % i
            cardfound = True
if not cardfound:
     print "No card found"

edited Aug 27, 2014 at 12:25

answered Aug 27, 2014 at 5:58

aquavitae

19.5k12 gold badges68 silver badges110 bronze badges

1 Comment

joegone Over a year ago

I'm trying to process the file until I find the card id and figure out what line it is on. I have another file which has a corresponding command. so card.txt has the cardids and command.txt has the corresponding commands. so line 1 (cardid) in card.txt will do command.txt line 1 (print "1") and so forth. I found this is the easiest way to manage 100 cardids and seperate commands.

Nagasaki45 · Accepted Answer · 2014-08-27 12:46:10Z

0

Looping through the lines of the list explicitly may be replaced with the in operator.

with open(...) as file:
    cards = file.readlines()
if card in cards:
    print('card found')
else:
    print('unknown card')

You may want to strip the '\n' from the end of each line, replacing the second line of the code above with:

cards = [line.strip() for line in file]

Lastly, if you just need to load the list of the cards once and perform checks against it many times use set instead of list (in will run much faster):

cards = set(line.strip() for line in file)

answered Aug 27, 2014 at 12:46

Nagasaki45

2,8901 gold badge24 silver badges28 bronze badges

Collectives™ on Stack Overflow

looking for a better solution to my script (python)

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related