为什么我的 Python 字典只返回最后一个值？

Question

I have an rfid reader which when scanned returns a UID as "backData"

I have my users (username and UID) stored in a text file.

I've managed to read the text file into a python dictionary, but when i scan my card, it is only accepting the last UID in the text file.

Text File:

164 168 124 90 42, user1
114 156 203 196 225, user2

Python Code:

for line in uid_file:
    info = line.split(",")
    key = info[0]
    uname = info[1]
    c = len(uname)-1
    uname = uname[0:c]
    uid_dict[key] = uname
    USER = [int(i) for i in key.split()]

    if backData == USER:
        f = open("/mnt/lock_logs/lock_log.csv", "a");
        print f
        value = ('\n') + uname
        myString = str(value)
        f.write(myString)
        f.close()
     else:
        print "Access Denied"

So if I scan the card assigned to user2, it works, but if I scan the card assigned to user1, I get Access Denied.

If i print the variable USER, it returns both UIDs from the text file. Any ideas on what I need to change??

Answer 1

I think this is because you continue to evaluate your for loop even after the user 1 is matched. Add a 'break' to the bottom of your if statement.

if backData == USER:
    f = open("/mnt/lock_logs/lock_log.csv", "a");
    print f
    value = ('\n') + uname
    myString = str(value)
    f.write(myString)
    f.close()
    break

I recreated your file and am able to get predicted behavior with the following code. Not that I hard coded backData and have tried it with both USER lists with success.

filename = 'uid.txt'

with open(filename) as uid_file:
    uid_dict={}

    backData = [164, 168, 124, 90, 42]
    no_matches = True

    for line in uid_file:
        info = line.split(",")
        key = info[0]
        uname = info[1]
        print info[0], info[1]
        c = len(uname)-1
        uname = uname[0:c]
        uid_dict[key] = uname
        USER = [int(i) for i in key.split()]

        if backData == USER:
            print "user matches"
            no_matches = False          
            break

    if no_matches:
        print "Access Denied"

Answer 2

Reanalyzing the code a bit, I am assuming that backData is an array, such as [114, 156, 203, 196, 225] .

Your code is going to loop through each line, checking the array against the stored key. It won't stop if it finds a match, and it will print Access Denied each time it doesn't match (not the same as if it had not found a match at all .)

A more detailed explanation:

If backData matched with user1, the following will happen in order:

1. Data for user1 is loaded.
2. backData is checked against the key for user1, matching.
3. \\nuser1 is appended to lock_log.csv
4. Data for user2 is loaded.
5. backData is checked against the key for user2, not matching.
6. Access Denied is printed.

If backData matched with user2, the following will happen in order:

1. Data for user1 is loaded.
2. backData is checked against the key for user1, not matching.
3. Access Denied is printed.
4. Data for user2 is loaded.
5. backData is checked against the key for user2, matching.
6. \\nuser2 is appended to lock_log.csv

If backData matched with neither, the following will happen in order:

1. Data for user1 is loaded.
2. backData is checked against the key for user1, not matching.
3. Access Denied is printed.
4. Data for user2 is loaded.
5. backData is checked against the key for user2, not matching.
6. Access Denied is printed again.