How to join two strings from different tuples but in the same index using Python?

Question

The tuples inside the file:

 (\'Wanna\', \'O\')
 (\'be\', \'O\')
 (\'like\', \'O\')
 (\'Alexander\', \'B\')
 (\'Coughan\', \'I\')
 (\'?\', \'O\')

Answer 1

Here's how I'd write this:

from ast import literal_eval
from itertools import tee

def pairwise(iterable): # from itertools recipes
    a, b = tee(iterable)
    next(b, None)
    return zip(a, b)

with open("a.txt") as f:
    for p0, p1 in pairwise(map(literal_eval, f)):
        if p0[1] == 'B' and p1[1] == 'I':
            print(' '.join(p0[0], p1[0]))
            break

---

Here's why:

Your file consists of what appear to be reprs of Python tuples of two strings. That's a really bad format, and if you can change the way you've stored your data, you should. But if it's too late and you have to parse it, literal_eval is the best answer.

So, we turn each line in the file into a tuple by mapping literal_eval over the file.

Then we use pairwise from the itertools recipes to convert the iterable of tuples into an iterable of adjacent pairs of tuples.

So, now, inside the loop, p0 and p1 will be the tuples from adjacent lines, and you can just write exactly what you described: if p0[1] is 'B' and it's followed by (that is, p1[1] is) 'I', join the two [0]s.

I'm not sure what you wanted to do with the joined string, so I just printed it out. I'm also not sure if you want to handle multiple values or just the first, so I put in a break.