CODEWITHSUNDEEP
python
user2669997
user2669997

Reputation:

python read file, print part of line that begins with a specific string

I have a text file which contains the following

steve:789852:1
sean:1234:1

I want to read the file and is the input from a user matches the first name then print out the middle number. I can do this for one line but not for the rest I keep getting

IndexError: list index out of range

I have tried a for loop and a while loop. The code I am using is below. any help please

x = 0
username = input('enter user name ')
file = open('user_details.txt', 'r')
count = len(open('user_details.txt').readlines())
while x < count:
    print(x)
    userFile = file.read().split('\n')[x]
    userArray = userFile.split(':')
    if (userArray[0] == username):
        print('password = '+userArray[1])
    x = x+1

Upvotes: 0

Views: 1206

Answers (3)

gaganso
gaganso

Reputation: 3011

readlines() takes the file pointer to the end of the file. So, when you try to read the file again using the same file reference, an empty string will be returned. Read the contents into a variable and iterate over it in the loop.

Upvotes: 0

Paul Rooney
Paul Rooney

Reputation: 21609

loop index variables are not generally needed in python, instead just use a for loop. A good rule of thumb is use a for loop when you know how many iterations there will be and a while when you don't.

username = input('enter user name ')

with open('user_details.txt', 'r') as f:
    for line in f:
        userArray = line.strip().split(':')
        if (userArray[0] == username):
            print('password = '+userArray[1])

Note the file is only opened once, and also closed properly using a with block. It also iterates only the lines of the file themselves once.

The key problem with your code is that you exhaust the file after the first iteration of the while loop.

The intention is to read each line of the file, but what you are doing is counting the lines of the file and looping that many times, then reading the entire file in each of those iterations. The file is not reopened between iterations so the first time the while loop iterates the file is read until the end. When you come round again in the second iteration of the while, there is nothing to read and you attempt to get the 1 index of that empty list, hence the index error.

It works for the first one by accident, because there is a 0th element in the list of all the lines.

Upvotes: 2

David Culbreth
David Culbreth

Reputation: 2776

Either use 

for line in file.readlines(): 
    ... do stuff ...

Or use 

lines = file.read().split('\n')
for line in lines:
    ... do stuff ...

Upvotes: 0

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