String + Variable + String formatting in Python

Question

I'm new to Python so please go easy, I'm sure my question has a very simple solution, that seems to be evading me. I'm trying to write a string to a file in this format:

"string1" variable "string2"

But it always seems to write "string2" "string1" variable

Here is my code:

inF = open("f:\test\Users.txt", 'r')
outF = open("f:\test\commands.txt", 'w')

for line in iter(inF):
    s = "{0} {1} {2}" .format("adduser ",line," password")
    outF.write(s)
inF.close()
outF.close()

I have also tried:

for line in iter(inF):
    outF.write("adduser " + lines + " password")

Output is always:

passwordadduser user.name

Answer 1

When you read a line from a file, it will always include the newline character. You then concatenate that directly. So in fact what you are seeing is this:

adduser line1\n
passwordadduser line2\n
passwordadduser line3\n

etc.

To fix this, strip the line when you read it:

for line in iter(inF):
    line = line.strip('\n')
    s = "{0} {1} {2}\n" .format("adduser ",line," password")

Answer 2

If you check, you'll see that the first two lines are like this:

adduser user1
 passwordadduser user2

You are reading the file line by line: line will contain a trailing "\n" so when you write it it goes to a new line, and you are not terminating what you write with a newline, so you get passwordadduser. Something like:

outF.write("{0} {1} {2}\n" .format("adduser ",line.strip()," password"))

Should fix your problem.

Answer 3

Please, use context managers to work with files. You should also handle new line symbols \n while reading and writing:

in_filename = "f:\\test\\Users.txt"
out_filename = "f:\\test\\commands.txt"

with open(in_filename, 'r') as in_fh, open(out_filename, 'w') as out_fh:
    for in_line in in_fh:
        out_line = "{} {} {}\n" .format("adduser", in_line.strip('\n'), "password")
        out_fh.write(out_line)

Users.txt:

us1
us2
us3

commands.txt:

adduser us1 password
adduser us2 password
adduser us3 password