On Mon, Feb 26, 2018 at 3:57 AM, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote: > On Mon, 26 Feb 2018 01:50:16 +1100, Chris Angelico wrote: > >> If you actually need character-by-character, you'd need "for character >> in fh.read()" rather than iterating over the file itself. Iterating over >> a file yields lines. > > Indeed. But I wonder if there's a performance cost/gain to iterating over > each line, rather than reading one char at a time? > > for line in file: > for c in line: > ... > > Too lazy to actually test it myself, but just tossing this idea out in > case anyone else cares to give it a try. >
Depends on the size of the file. For a small file, you could read the whole thing into memory in a single disk operation, and then splitting into lines is a waste of time; but for a gigantic file, reading everything into RAM means crazy-expensive transfer/copy, so it'd be HEAPS more efficient to work line by line - particularly if you don't need the whole file. But if you indeed want to cut the process off, having nested loops means a simple "break" won't work. So that's a different consideration. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
