read next line after a matching line in python

Question

I am trying to go to next line after a match in python. I have a file:

ratio of lattice parameters  b/a  c/a
    1.000000000000    1.000000000000
lattice parameters  a b c  [a.u.] 
    9.448629942895    9.448629942895    9.448629942895

So, when I have "lattice parameters" at the beginning of line, I will read the next line (e.g. 9.448629942895 9.448629942895 9.448629942895) I am doing:

#!/usr/bin/python3
import sys

inpf = str(sys.argv[1])
print (inpf)
with open(inpf, "r") as ifile:
    for line in ifile:
        if line.startswith("lattice parameters"):
            print(line.strip())
            next(ifile)
            return next(ifile)

as is in the accepted answer here. But, in my case, it is giving error:

python xband.py AlSi2S2.sys 
  File "xband.py", line 11
    return next(ifile)
SyntaxError: 'return' outside function

What I am doing wrong here? NB: I want to go to and read next line. I have no special fascination on "return" I am using Python 3.4.2

Answer 1

Try:

with open(inpf, "r") as ifile:
    for line in ifile:
        if line.startswith("lattice parameters"):
            print(next(ifile, '').strip())

next(iterator[, default])
Retrieve the next item from the iterator by calling its next() method. If default is given, it is returned if the iterator is exhausted, otherwise StopIteration is raised.

Answer 2

You are using a return statement outside of a function. For the code to work you schould either get rid of the return next(ifile) line or make a function in your script and call it.