On Fri, 28 Oct 2005 20:03:17 -0700, [EMAIL PROTECTED] (Alex Martelli) wrote:
>Mike Meyer <[EMAIL PROTECTED]> wrote: > ... >> Except if you can't read the file into memory because it's to large, >> there's a pretty good chance you won't be able to mmap it either. To >> deal with huge files, the only option is to read the file in in >> chunks, count the occurences in each chunk, and then do some fiddling >> to deal with the pattern landing on a boundary. > >That's the kind of things generators are for...: > >def byblocks(f, blocksize, overlap): > block = f.read(blocksize) > yield block > while block: > block = block[-overlap:] + f.read(blocksize-overlap) > if block: yield block > >Now, to look for a substring of length N in an open binary file f: > >f = open(whatever, 'b') >count = 0 >for block in byblocks(f, 1024*1024, len(subst)-1): > count += block.count(subst) >f.close() > >not much "fiddling" needed, as you can see, and what little "fiddling" >is needed is entirely encompassed by the generator... > Do I get a job at google if I find something wrong with the above? ;-) Regards, Bengt Richter -- http://mail.python.org/mailman/listinfo/python-list
