looping over a big file

[Roy Smith]

"martian" <nospam at hetnet.nl> wrote:
> 1) how does python handle:
> 
> > for line in big_file:
> 
> is big_file all read into memory or one line is read at a time or a buffer
> is used or ...?

The "right" way to do this is:

for line in file ("filename"):
   whatever

The file object returned by file() acts as an iterator.  Each time through 
the loop, another line is read and returned (I'm sure there is some 
block-level buffering going on at a low level).

> 2) is it possible to advance lines within the loop? The following doesn't
> work:
> 
> > for line in big_file:
>          line_after  = big_file.readline()

You probably want something like:

for line in file ("filename"):
   if skipThisLine:
      continue