Can't Print A Specific Line From Text File

So I currently have this code to read an accounts.txt file that looks like this: username1:password1 username2:password2 username3:password3 I then have this (thanks to a member h

Solution 1:

username and password are strings. When you do this to a string, you get the first character in the string:

username[0]

Don't do that. Just print username.

Some further explanation. credentials is a list of lists of strings. It looks like this when you print it out:

[['username1', 'password1'], ['username2', 'password2'], ['username3', 'password3']]

To get one username/password pair, you could do this: print credentials[0]. The result would be this:

['username1', 'password1']

Or if you did print credentials[1], this:

['username2', 'password2']

You can also do a thing called "unpacking," which is what your for loop does. You can do it outside a for loop too:

username, password = credentials[0]
print username, password

The result would be

username1 password1

And again, if you take a string like 'username1' and take a single element of it like so:

username[0]

You get a single letter, u.

Solution 2:

First, I'd like to say if this is your second day programming, then you're off to a good start by using the with statement and list comprehensions already!

As the other people already pointed out, since you are using [] indexing with a variable that contains a string, it treats the str as if it were an array, so you get the character at the index you specify.

I thought I'd point out a couple of things:

1) you don't need to use f.readline() to iterate over the file since the file object f is an iterable object (it has the __iter__ method defined which you can check with getattr(f, '__iter__'). So you can do this:

withopen('accounts.txt') as f:
    for l in f:
        try:
            (username, password) = l.strip().split(':')
            print username
            print password
        except ValueError:
            # ignore ValueError when encountering line that can't be# split (such as blank lines).pass

2) You also mentioned you were "curious if there's a way to print only the first line of the file? Or in that case the second, third, etc. by choice?"

The islice(iterable[, start], stop[, step]) function from the itertools package works great for that, for example, to get just the 2nd & 3rd lines (remember indexes start at 0!!!):

from itertools import islice
start = 1; stop = 3withopen('accounts.txt') as f:
    for l in islice(f, start, stop):
        try:
            (username, password) = l.strip().split(':')
            print username
            print password
        except ValueError:
            # ignore ValueError when encountering line that can't be# split (such as blank lines).pass

Or to get every other line:

from itertools import islice
start = 0; stop = None; step = 2withopen('accounts.txt') as f:
    for l in islice(f, start, stop, step):
        try:
            (username, password) = l.strip().split(':')
            print username
            print password
        except ValueError:
            # ignore ValueError when encountering line that can't be# split (such as blank lines).pass

Spend time learning itertools (and its recipes!!!); it will simplify your code.