how do I "peek" into the next line?

[Steven Bethard]

les_ander at yahoo.com wrote:
> now suppose I have read the first line already.
> then I read the second line and notice
> that there is a ">" in front (my special character)
> then I want the put back the second line into the
> file or the stdin.

Amended iterator class example using my peekable recipe:

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

Note that because I wrap the file iterator with a peekable[1] object, 
the lines aren't consumed when I test them.  So to access the remaining 
lines, I just use the iter field of the strangefileiter object.

Steve

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