Question

I need to keep calling sync for each line in file.txt until the function returns non-zero(that is when it fails). Currently I plan to do the following.

for line in file("file.txt"):
        change=int(line)
        cp_success=sync(change) #check the return value of function sync
        if cp_success!=0 : 
            break               #Try using a break statement

Is there a better way or one-liner?

Answer 1

Well, almost in one line (if you allow me to import the itertools module):

[ x for x in itertools.takewhile(
    lambda line: sync(line) == 0,    # <- predicate
    open("file.txt")) ]              # <- iterable

Example w/o file:

>>> import itertools
>>> def sync(n):
...   if n == 3: return -1 # error
...   return 0

>>> lines = [1, 2, 3, 4, 5, 6]
>>> [ x for x in itertools.takewhile(lambda x: sync(x) == 0, lines) ]
[1, 2]

But you really should not obscure things, so why not just:

with open("file") as fh:
    for line in fh:
        if not sync(int(line)) == 0:
            break