CODEWITHSUNDEEP
pythonloops
Kevin R.
Kevin R.

Reputation: 602

returning value outside a for loop

I have this text file:

[admin]# cat /etc/passwd
root:!:0:0::/:/usr/bin/ksh
daemon:!:1:1::/etc:
bin:!:2:2::/bin:
sys:!:3:3::/usr/sys: 
adm:!:4:4::/var/adm:
uucp:!:5:5::/usr/lib/uucp: 
guest:!:100:100::/home/guest:
nobody:!:4294967294:4294967294::/:
lpd:!:9:4294967294::/:
lp:*:11:11::/var/spool/lp:/bin/false 
invscout:*:200:1::/var/adm/invscout:/usr/bin/ksh
nuucp:*:6:5:uucp login user:/var/spool/uucppublic:/usr/sbin/uucp/uucico
paul:!:201:1::/home/paul:/usr/bin/ksh
jdoe:*:202:1:John Doe:/home/jdoe:/usr/bin/ksh

and some code here

with open(file) as f2:
            for lines in f2:
                if "cat /etc/passwd" in lines:
                    for i in range(3):
                        cat = f2.readline()
                        print(cat)

if it finds the string "cat /etc/passwd", it will store the next couple of lines inside the variable cat

output:

root:!:0:0::/:/usr/bin/ksh
daemon:!:1:1::/etc:
bin:!:2:2::/bin:

This is the case if I call cat from inside the for loop. If I call it outside of the for loop, I only get the last line :

bin:!:2:2::/bin:

I assume the line for i in range(3) is the reason for this. is there a way I can call cat outside the loops and have it return each of the lines I want printed?

Upvotes: 0

Views: 493

Answers (4)

qvpham
qvpham

Reputation: 1938

The mixing of iteration (for lines in f2) and read method (f2.readline) is not nice. I have a other solution with itertools.islice, which only uses iteration

from itertools import islice

with open(file) as f2:
    for line in f2:
        if "cat /etc/passwd" in lines:
            cat = list(islice(f2, 3))

print cat

cat is a list like the answer of Alex

Upvotes: 0

Kodain
Kodain

Reputation: 1

Have you tried this ?

cat = ''
with open(file) as f2:
            for lines in f2:
                if "cat /etc/passwd" in lines:
                    for i in range(3):
                        cat += f2.readline()
print(cat)

Upvotes: 0

Peter1807
Peter1807

Reputation: 184

For each iteration you overwrite the last value of cat.

Inside of the loop, you print each time before you overwrite. Outside of the loop, you only print its last value.

You could store your results in an array

with open(file) as f2:
        for lines in f2:
            if "cat /etc/passwd" in lines:
                cat = []
                for i in range(3):
                    cat.append(f2.readline())
                    print cat[i] 

for x in cat:
    print x

Upvotes: 1

Alex Hall
Alex Hall

Reputation: 36033

cat = []
with open(file) as f2:
    for lines in f2:
        if "cat /etc/passwd" in lines:
            for i in range(3):
                cat.append(f2.readline())

print cat

Read about python lists.

Upvotes: 3

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