how do I "peek" into the next line?

[Steven Bethard]

Skip Montanaro wrote:
>     les> suppose I am reading lines from a file or stdin.  I want to just
>     les> "peek" in to the next line, and if it starts with a special
>     les> character I want to break out of a for loop, other wise I want to
>     les> do readline().
> 
> Create a wrapper around the file object:
> 
[snip]
> 
> Of course, this could be tested (which my example hasn't been)

If you'd like something that works similarly and has been tested a bit, 
try one of my recipes for peeking into an iterator:

http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/304373

You also might consider writing an iterator wrapper for a file object:

 >>> class strangefileiter(object):
...     def __init__(self, file):
...         self.itr = iter(file)
...     def __iter__(self):
...         while True:
...             next = self.itr.next()
...             if not next or next.rstrip('\n') == "|":
...                 break
...             yield next
...
 >>> file('temp.txt', 'w').write("""\
... some text
... some more
... |
... not really text""")
 >>> for line in strangefileiter(file('temp.txt')):
... 	print repr(line)
...
'some text\n'
'some more\n'
 >>> file('temp.txt', 'w').write("""\
... some text
... some more
...
... really text""")
 >>> for line in strangefileiter(file('temp.txt')):
... 	print repr(line)
...
'some text\n'
'some more\n'
'\n'
'really text'


Steve