Reading and writing magnetic card reader input with Python

Question

I am using a magnetic card reader to read input from magnetic cards. The cards have three tracks, but each track holds the same exact data on each track. When I swipe a card, the first track is written to a variable and then written to a csv file for later use. The problem is that after each track is read, a return character is entered so that the while loop I am running reads and writes the same data three times for each swiped card. Is there any way that I can make the first two returns null so that I only get the data written once or is there any other way that I can go about doing this so that I only get the text once and data written once for each card? If you have any questions about this let me know. I tried to word it is clearly as possible. I will also include the code.

    #Card Reader
    import getpass
    import datetime
    import csv
    import os
    full_date = str(datetime.datetime.now())
    short_date = full_date[5:10]
    print(short_date)
    while True:
        while True:
            try:
                ID = getpass.getpass(prompt = 'Please swipe your ID card. ')
                if os.path.exists('.\attendance.csv'):
                    student_number = open('.\attendance.csv', 'a')
                    student_number.write(ID[1:10] + '\n')
                    print('')
                else:
                    student_number = open('.\attendance.csv', 'w')
                    student_number.write(ID[1:10] + '\n')
                    print('')
            except KeyboardInterrupt:
                break

I had more code in between at one point but took it out and just never caught it. I was going to clean it up later. So, there is no reason for it. Thanks for catching that though! — law10, Sep 01 '15 at 18:24
If the values are identical and of same length, why not grab the list of values and break after `n` index where `n` is the length of the desired value? — Juxhin, Sep 01 '15 at 18:30

score 1 · Answer 1 · answered Sep 01 '15 at 18:29

1

You can use a counter to keep track of the number of times the value has been returned.

counter = 0
while True:
    ID = getpass.getpass(prompt = 'Please swipe your ID card.')
    if counter < 3:
        counter += 1
    else:
        counter = 0
        if os.path.exists('.\attendance.csv'):
            student_number = open('.\attendance.csv', 'a')
            student_number.write(ID[1:10] + '\n')
            print('')
        else:
            student_number = open('.\attendance.csv', 'w')
            student_number.write(ID[1:10] + '\n')
            print('')

Since you are developing a card reader, it is safe to assume that another card swipe will not interfere with the counter and each student's attendance would be written only once.

answered Sep 01 '15 at 18:29

Divij Bindlish

325
1
8

I was thinking of something like this when trying to solve it myself. I tried implementing it and then tried implementing yours also. Unfortunately this did not fix the problem. It is probably my fault for not explaining well. When I swipe a magnetic card it does the following: 1. Outputs a string of text (I believe 12 or 13 characters long) 2. The card (or card reader, I am not sure which is doing this) enters a return character 3. The same text in the first string is printed again on the next line because of the return character entered 4. Steps 2 and 3 are then repeated a second time. – law10 Sep 03 '15 at 17:42
Because of this, the program ends up running three times and recording the number 3 times for each card instead of just once. Is there a way that I can make it stop reading after the first track or somehow make the return characters null so that all 3 tracks are recorded as one variable? – law10 Sep 03 '15 at 17:44

Reading and writing magnetic card reader input with Python

1 Answers1